Article

A systematic study of the nine hydrogen-bonded dimers involving NH3, OH2, and HF

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Abstract

The nine H-bonded dimers of NH3, OH2, and HF have been calculated by ab initio molecular orbital theory at the 6-31G* level with geometry optimization. Calculated dimerization energies (kilocalories/mole) are: H3N⋯HNH2, 2.9; H3N⋯HOH, 6.5; H3N⋯HF, 12.2; H2O⋯HNH2, 2.8; H2O⋯HOH, 5.6; H2O⋯HF, 9.2; HF⋯HNH2, 2.6; HF⋯HOH, 4.0; HF⋯HF, 5.9. Energies and geometries are compared with available experimental and ab initio values from the literature. The 6-31G* results are found to be internally consistent and of reasonable accuracy. The paucity of experimental measurements on gas-phase dimers makes the present set of results of special significance for understanding the mechanism of hydrogen bonding, and for stimulating further experimental work.

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The CO bond length and the quadratic, cubic and quartic stretching force constants, calculated ab initio using the unscaled 4–31G basis set with full geometry optimization, are reported for three series of monosubstituted carbonyl compounds in which the atom directly bonded to the carbonyl carbon is another carbon, a nitrogen, or an oxygen atom, respectively. The data are analyzed in terms of the In ƒ versus In re relationship, and also the generalized power functions and exponential functions proposed by Herschbach and Laurie. Not only does the atom directly bonded to the carbonyl carbon affect the magnitude of re and the force constants, but the rest of the substituent group is found to be capable of exerting an even greater influence. Within each series of compounds the overall progression from the shortest to the longest CO bonds is tentatively attributed to a diminishing electron density in the bonding region.
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Gas-phase reactions of vinylformate with the hydroxide ion and its hydrate have been studied using both the AM1 and ab initio MO calculations. Four competitive reaction pathways (α-H+ abstraction, vinyl-H+ abstraction, BAC2, and nucleophilic vinyl substitution (NVS)) are found to be possible. In the reactions with OH− the four processes are all exothermic, whereas in the reactions with hydrated OH− only the nucleophilic reactions proceed exothermically. The NVS reaction has the greatest exothermicity in both reactions with bare and hydrated OH−. Solvation of the hydroxide ion leads to decreases in reactivities and reactivity differences between BAC2 and NVS paths due to the smaller energy gaps between intermediates formed along the reaction coordinates, in addition to a mechanistic change in the vinyl-H+ abstraction. The reactivities of nucleophilic reactions are discussed with the HOMO (nucleophile)-LUMO (substrate) interactions in the initial states. The AM1 results tend to describe anions incorrectly and show substantial disagreement in the heats of reaction with those obtained from ab initio calculations.
Article
Electronic population changes and the evolution of the contour maps of the charge density and its Laplacian are used to study the polarizability of hydrogen bonds as a function of the position of the proton within the hydrogen bond. Standard ab initio molecular orbital theory at the 4–31G level (44-31G* for sulphur) has been used to study the complexes between the acceptors, formaldehyde and thioformaldehyde, and the donors, hydrogen fluoride and the ammonium cation. A number of important conclusions for the interpretation of infrared spectra are discussed.
Article
Several (NH4)+(NH3)n(H2O)w mixed clusters have been studied theoretically using the semiempirical AM1 method. In good agreement with the experimental data, our results show that while the primary solvation shell surrounding the NH+4 central core is preferentially formed by ammonia molecules, water molecules are preferred in the next solvation shell. The reasons for this preferential solvation are discussed through an analysis of the hydrogen bonds which are formed. Finally, AM1 is shown to be an adequate method for reproducing the experimental results in systems where the correct evaluation of hydrogen bonds is of major importance.
Article
Ab initio calculations have been carried out for ammonia dimers with 4-31G and 6-31G* basis sets. The results are corrected for basis-set superposition error. For the ammonia dimer, the stability of the linear form is comparable to that of the cyclic form. The localized orbitals for both dimers are discussed.
Article
Two stationary points have been found on the 4—31G energy hypersurface of CO2⋯HF; the linear structure of the complex corresponds to a real minimum, whereas the Cs structure represents a saddle point, Geometric and energy characteristics of the linear complex have been recalculated at the 6—31G* level with inclusion of dispersion energy (polarizability model). Finally, the formation of the complex has been treated thermodynamically.
Article
Using the 4-31G basis set augmented with polarization functions on the S-atom all geometrical parameters have been optimized for the planar chain and ring conformers (related by 180° rotation of the OH, SH or NH group) of acrylic acid, the three monothioperformic acids,α-hydroxyacrolein, formyl and thioformylhydroxylamine, glyoxalmonoimine, formimidol and glyoxalmonooxime. The changes in bond lengths and bond angles which accompany the conversion of the chain into the ring conformer are classified under ten headings for a total of eight four-membered, nine five-membered and three six-membered ring systems. Systematic trends are found, indicative of electron transfer, which support the hypothesis that there is a hydrogen-bonding type of interaction in the four-as well as in the five- and six-membered rings. The change in total molecular energy for the conversion reaction is divided up into distortion and bonding energy components, and each partitioned in terms of the expectation energy differencnes ΔEK, ΔVee, ΔVnn and ΔVen. The nature of the distortion and bonding steps, whether attractive-dominant or repulsive-dominant, is correlated with ring size and the presence (or absence) of heavy atoms external to the ring. The internuclear disease OH, O…O and H … O in the OH … O(=C) hydrogen bridge are compared with experimental values for intermolecular hydrogen bonds, and the present findings are discussed in relation to studies in the literature on electron density distributions and chages in Mulliken gross electronic populations.
Article
Several minimal (7, 3/3) Gaussian basis sets have been used to calculate the energies and some other properties of CH4 and H2O. Improved basis sets developed for these molecules have been extended to NH3 and HF and employed to H2CO and CH3OH. Interaction energies between XHn molecules have been calculated using the old and the new minimal basis sets. The results obtained with the new basis sets are comparable in accuracy to those calculated with significantly more extended basis sets involving polarization functions. Binding energies calculated using the counterpoise method are not much different for the new and the old minimal basis sets, and are likely to be more accurate than the results of much more extended calculations.
Article
Electron photodetachment of solvated anions of the form ROHF- has been undertaken. Observation or non-observation of photodetachment provides information about the location of the bridging proton, i.e. whether the complex has the structure ROH·F- or RO-·HF. Where photodetachment is observed, the experimental detachment threshold energy yields the solvation energy for the corresponding free anion.
Article
A simple model of “superexchange” interactions, taken from phenomena of magnetic ordering in non-conducting 3d-solids, is found to account quantitatively for stereospecificity and binding energy in the dimers (HF)2 and (H2O)2 and the moleculer complex H2O·HF. The exchange unit is formed by two hydrogen atoms on different molecules and the nearest heavier atom. The results are compared with those obtained on the basis of ab initio analyses with the largest available basis sets.
Article
The influence of the β−-decay on the N—HN hydrogen bond in the tritiated-ammonia dimer and in tritiated-methyl-amine-ammonia has been studied by ab initio LCAO SCF MO calculations. The hydrogen bond, except in the ammonia dimer, is predicted to be broken following the β−decay.
Article
The microwave spectrum of the heterodimer HCN…HF is reported, the collinearity of the nuclei established, and r0(N…F)=2.796 Å obtained. From the Stark effect, μ0(HCN…HF)=5.59 ± 0.02 D which indicates an enhancement of 0.78 D over the vector sum of the monomer values.
Article
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Ab initio LCAO‐SCF molecular orbital calculations have been carried out with an extensive basis set to determine the stabilization energies of a cyclic trimer, a cyclic tetramer, and various noncyclic oligomers of water. The cyclic trimer is shown to be less stable than the noncyclic one. It is concluded that appreciable nonadditive effects are not present in cyclic polymers of water and that these structures show no special stability (compared to noncyclic ones) other than that to be expected from their extra hydrogen bond. Finally, the results of these and similar calculations are used to calculate the lattice energy of ice I, which agrees well with the experimental value.
Article
Full-text available
The Hartree‐Fock energy of the water dimer has been computed for 216 different nuclear configurations using the basis set given in the first paper of this series. Near the equilibrium configuration, a calculation was carried out using a large Gaussian basis set with optimized orbital exponents for the oxygen 3d ‐ and 4f ‐type and hydrogen 2p ‐ and 3d ‐type functions in order to get results close to the Hartree‐Fock limit. In the vicinity of the equilibrium configuration the mechanism for binding of the dimer is analyzed with the help of the bond energy analysis formalism. The importance of polarization (internal charge transfer), as pointed out previously by a number of authors, is clearly evident. The computed energies have been used to derive a simple analytical expression that reproduces the Hartree‐Fock potential energy surface to a high degree of accuracy. This analytical potential is compared with the empirical effective pair potentials proposed by Rowlinson and Ben‐Naim and Stillinger for the description of water in the condensed phase. We report preliminary results for Monte Carlo simulation of the liquid state of water using the computer program of Barker and Watts and our analytical Hartree‐Fock two‐body interaction potential. At the experimental mass densities we considered 27 water molecules in a cube with periodic boundary conditions at temperatures of 277, 298, and 348°K. The resulting pair correlation functions gO�H(2) (hydrogen bond distribution) and gO�O(2) (oxygen‐oxygen distribution) are in agreement with experimental data. It should be strongly emphasized that the properties are computed without any recourse to semiempirical data.
Article
The theory of molecules in molecules introduced in previous articles is applied to study the hydrogen bonding interaction in the linear configuration of the dimer of FH. The transfer of localized molecular orbitals as well as the majority of the additional approximations introduced to save computational time can be justified and shown to lead to results in good agreement with those of ab initio calculations. An energy analysis of the effect of the hydrogen bond formation on the localized orbitals is given. It is seen that the effect is small, the major contribution to the binding energy is given by a first order perturbation treatment.
Article
An extended basis set of atomic functions expressed as fixed linear combinations of Gaussian functions is presented for hydrogen and the first‐row atoms carbon to fluorine. In this set, described as 4–31 G, each inner shell is represented by a single basis function taken as a sum of four Gaussians and each valence orbital is split into inner and outer parts described by three and one Gaussian function, respectively. The expansion coefficients and Gaussian exponents are determined by minimizing the total calculated energy of the atomic ground state. This basis set is then used in single‐determinant molecular‐orbital studies of a group of small polyatomic molecules. Optimization of valence‐shell scaling factors shows that considerable rescaling of atomic functions occurs in molecules, the largest effects being observed for hydrogen and carbon. However, the range of optimum scale factors for each atom is small enough to allow the selection of a standard molecular set. The use of this standard basis gives theoretical equilibrium geometries in reasonable agreement with experiment.
Article
Accurate SCF calculations have been carried out to investigate the potential of interaction for pairs and triplets of water molecules. The most stable pair configuration involves a linear hydrogen bond of length ROO = 3.00Å and strength 4.72 kcal/mole. Three‐molecule nonadditivities are large in magnitude and vary in sign according to the hydrogen‐bond pattern involved. In both aqueous liquids and solids, the net trimer nonadditivity effect amounts to increased binding energy, decreased neighbor distance, and slightly enhanced tendency toward perfect tetrahedral coordination symmetry. The nonadditivity furthermore is inconsistent with the phenomenology of simple mutual electrostatic polarization between neighboring molecules.
Article
The energy surface of dimeric water is studied for the linear and bifurcated geometries within the SCF MO LCGO framework, using a gaussian basis set to approximate the avefunction. The minimum energy geometry of dimeric water is found to be linear with a hydrogen bond distance of 2.04Å and a binding energy of 4.84 kcal/mole (experimental 5.0 kcal/mole). The dipole moment was computed to be −1.69 au.
Article
The hydrogen bond energy of the isolated linear water dimer has been investigated with the use of the bond orbital approximation. This approach provides a simple description of the relative contributions from electrostatic, overlap repulsion, and charge transfer effects. The basis set used is a minimum basis of Slater atomic orbitals. The hydrogen bond energy obtained is in reasonable agreement with the values obtained from SCF calculations.
Article
Hartree—Fock wavefunctions are presented for the LiH(X1Σ+), BeH(X2Σ+), BH(X1Σ+), CH(X2&Pgr;r), NH(X3Σ−), OH(X2&Pgr;i), and HF(X1Σ+) molecules. These are the analytic self-consistent-field wavefunctions obtained from the solutions of the Hartree—Fock—Roothaan equations. Large sets of Slater-type functions centered on both nuclei were used as the expansion basis, and extensive optimization of the orbital exponents has been carried out. The total energies obtained for Re(exptl) are −7.98731, −15.15312, −25.13137, −38.27935, −54.97806, −75.42083, and −100.07030 hartrees, respectively, for the AH hydrides listed above. The first ionization potentials, which are obtained from the Hartree—Fock energy differences between AH and AH+ systems, are 7.02, 8.14, 8.45, 10.08, 12.82, 11.44, and 14.54 eV, respectively. In addition, potential curves, spectroscopic constants, and certain other energetic quantities are presented. Crude estimates of the correlation energy of the first-row hydrides are made and such quantities are compared within the series and with their respective united and separated atoms. These results suggest that the changes in correlation energy of AH relative to the correct united atom is independent of which hydride is involved and the change is small.
Article
The geometry and vibrational frequencies of the water dimer are calculated using ab initio LCAO-SCF theory. Most of the results were obtained using a split valence basis set. Some calculations with a larger basis set having polarization functions are also reported. The findings are somewhat dependent on the basis set with the split valence basis set giving too strong a hydrogen bond and consequently force constants which are too large. The intramolecular frequency shifts are in reasonable agreement with experimental results. The low frequency intermolecular vibrations are also determined and are qualitatively consistent with the infrared spectrum of liquid water.
Article
A simple level of ab initio molecular orbital theory with a split-valence shell basis with d-type polarization functions (6-31G*) is used to predict equilibrium geometries for the ground and some low-lying excited states of AHn molecules and cations where A is carbon, nitrogen, oxygen or fluorine. The results are shown to be close to the limit for single determinant wave functions in cases where corresponding computations with more extensive bases are available. Comparison with experimental results also shows good agreement although a systematic underestimation of bond lengths up to 3 per cent is evident. For systems where no experimental data are available, the results provide predictions of equilibrium geometry.
Article
Ab initio LCAO&sngbnd;MO&sngbnd;SCF calculation for the dimeric H2O system is carried out with a minimal Slater basis set with exponents optimized for H2O. The most stable linear dimer is found to have an O···H distance of 1.80 Å, with the proton-acceptor molecule perpendicular to the donor molecule and bent by 54° trans with respect to the end OH bond of the donor. The stabilization energy calculated is about 6.55 kcal/mole. The changes in the length and the stretching force constant of the donor O&sngbnd;H bond are also discussed. A population analysis shows that the stabilization at a larger O···H distance (>2.3 Å) is essentially electrostatic, while at a smaller distance, the charge transfer becomes increasingly important.
Article
Ab initio SCF calculations with a minimal STO−3G basis set have been performed to determine the equilibrium structures and energies of dimers having formamide as the proton donor molecule and either water or formaldehyde as proton acceptor molecules. The structures of dimers in which the N−H proton ’’s−trans’’ to the carbonyl group is hydrogen bonded (t dimers) are consistent with structures anticipated from the general hybridization model. In these dimers, there is essentially free rotation of the proton acceptor molecule about the intermolecular line. When hydrogen bond formation involves the ’’s−cis’’ proton (c dimers), a single equilibrium formamide−water and formamide−formadehyde dimer exists, the structure of which is strongly influenced by the secondary factors of dipole alignment and long−range interaction. These factors are also responsible for the increased stability of c dimers relative to t dimers. A set of 1:2 formamide:water trimers has been constructed from the equilibrium formamide−water dimers, in which the formamide molecule forms two hydrogen bonds. Only in three open−chain trimers are the hydrogen bonds stronger than those of the corresponding dimers. CI calculations have also been performed to determine the effect of hydrogen bond formation on n→π∗ transition energies in the dimers and trimers. The n→π∗ transition energy of the proton acceptor formaldehyde molecule increases in the formamide−formaldehyde dimers. In these dimers, the magnitude of the blue shift is determined by the dimer hydrogen bond energy. The formamide n→π∗ band is also blue shifted to some extent in the formamide−water and formamide−formaldehyde dimers, even though the n→π∗ transition originates in the proton donor molecule. The blue shift of the formamide n→π∗ band in the open−chain trimers having formamide as the central molecule is equal to the sum of the blue shifts in the corresponding dimers.
Article
Ab initio minimal basis LCAOSCF molecular orbital calculations have been performed on (H2O2)2 and on the mixed H2O�H2O2 dimers. The equilibrium structures and energies of these dimers are presented and analyzed. A cyclic structure is predicted to be most stable for (H2O2)2, while open chain structures are predicted for the mixed dimers. The effect of dimerization on the trans barrier to internal rotation in H2O2 is also discussed.
Article
The ground state binding energy (BE), rotational and vibrational energy levels, and line strengths for radiative transitions between some of these energy levels are calculated for the [H2O]2 molecule. These quantities are computed for three intermolecular potentials published for the [H2O]2 molecule, two of which were calculated by MO SCF techniques and one which was derived from an empirical point charge model for the water molecule. The value of BE calculated for two of the potentials is approximately 6 kcal∕mole, and for the third is approximately 3 kcal∕mole. The total concentration of [H2O]2 in equilibrium with H2O vapor is calculated for the sets of energy levels determined for these potentials. Results are compared with available experimental data. Using calculated values of line strengths and experimental data for the integrated absorptions for two rotational transitions, an independent value is deduced for the equilibrium concentration of [H2O]2 in fair agreement with values calculated from two of the intermolecular potentials. The theoretical calculations for BE and the equilibrium concentration of [H2O]2 are also compared with those obtained from analysis of experimental data for the second virial coefficient B2(T) of H2O vapor. The theoretical values for BE bracket the value of 3–4 kcal∕mole obtained from analysis of the data for B2(T). A discussion of our results is presented, along with suggestions for experimental work to search for the spectrum of [H2O]2 in the absorption spectrum of H2O vapor.
Article
Quantitative gas-phase infrared intensity measurements for NH3 in the 3 μ region have been used to determine the following quantities: the energy of hydrogen bonding (4.5 ± 0.4 kcal/mole), the factor by which the integrated region intensity was increased because of hydrogen bonding (∼25), and the ratio (7.0±0.5) of the sum of the squares of the vibrational matrix elements for the transitions (010000 → 110000) and (010000 → 011100) to the sum of the squares for the transitions (000000 → 100000) and (000000 → 001100).
Article
The hydrogen bond N·HO between the water and ammonia molecules has been investigated ab initio using the SCF LCAO MO method. The minimal and extended basis sets of Slater type orbitals were used. It was found that the energy of the hydrogen bond is equal to 6.44 kcal/mole and the equilibrium separation of the oxygen and nitrogen atoms in the dimer is 5.72 au. At this intermolecular distance there is only one minimum in the potential energy curve for the motion of proton.
Article
The theory of molecules in molecules introduced in previous articles is applied to study the hydrogen bonding interaction between an ammonia molecule as proton acceptor and a water molecule as proton donor. The localized orbitals which are assumed to be least affected by the formation of the hydrogen bond are transferred unaltered from calculations on the fragments NH3 and H2O, the remaining orbitals are recalculated. A projection operator is used to obtain orthogonality to the transferred orbitals. Additional approximations have been introduced in order to be able to save computational time. These approximations can be justified and are seen to lead to binding energies and bond lengths which are in satisfactory agreement with the SCF values. The point charge approximation for the calculation of the interaction energy between the two sets of transferred localized orbitals is, however, not applicable in this case. An energy analysis of the effect of the hydrogen bond on the localized orbitals of the two fragments is given.
Article
Least‐squares representations of Slater‐type atomic orbitals as a sum of Gaussian‐type orbitals are presented. These have the special feature that common Gaussian exponents are shared between Slater‐type 2s and 2p functions. Use of these atomic orbitals in self‐consistent molecular‐orbital calculations is shown to lead to values of atomization energies, atomic populations, and electric dipole moments which converge rapidly (with increasing size of Gaussian expansion) to the values appropriate for pure Slater‐type orbitals. The ζ exponents (or scale factors) for the atomic orbitals which are optimized for a number of molecules are also shown to be nearly independent of the number of Gaussian functions. A standard set of ζ values for use in molecular calculations is suggested on the basis of this study and is shown to be adequate for the calculation of total and atomization energies, but less appropriate for studies of charge distribution.
Article
It is shown that the data of Kuipers on the absorption of the HF monomer lines can be interpreted if the line contour is expressed in a modified Lorentz form alpha=alpha0a2p2[(v-v0)1.8+a2p2]-1 The apparent absorbance at the line centers has been measured under such circumstances that the temperature variation of alpha0a2 can be obtained. It is shown that the line breadth parameter, a, has the temperature variation expected if resonant dipole intermolecular forces are for the most part responsible for the line breadth. The absorption computed from the modified Lorentz expression between the monomer lines is sometimes considerably less than the absorption that is measured. The difference is attributed to HF dimer. There result three dimer bands. The strongest is broad and featureless with a peak near 3857 cm-1, the two other bands have PQR structures with Q branch peaks at 3895 and 3965 cm-1. The temperature dependence of the dimer absorption indicates a heat of decomposition of about 6 kcal/mole.
Article
Ab initio minimal basis LCAO SCF molecular orbital calculations have been performed to determine the energies and configurations of small groups of water molecules. It is found that polymers having OH3. OH3. OH3. chains are preferred, and that hydrogen bond energies deviate considerably from additivity. Cyclic structures are predicted to be most stable for the trimer and higher polymers.
Article
The proton donor ability of HCl and HF are compared by carrying out ab initio molecular orbital studies on complexes of these proton donors with a number of proton acceptors. In addition, the structure and H-bond energy of the HCl dimers and HCl-HF complexes are predicted.
Article
The energy hypersurface of the system NH3 · H2O is investigated for a number of different internuclear geometries. In the minimum energy structure involving a linear hydrogen bond, NH3 acts as proton acceptor. The binding energy of the system is calculated to be 6.28 kcal/mole and the bond distance d(NO) to be 3.07 Å. The potential energy curve of the inversion of the hydrogenbonded NH3 is computed and discussed.
Article
The hydrogen‐bond energy and the most stable structure of the dimeric H2O system are calculated by the LCAO MO SCF method using a medium‐sized Gaussian orbital basis set. The most stable structure, found by a limited variation of the interatomic coordinates, is a linear hydrogen bond (stabilization energy 12.6 kcal mole−1) with an H⋅⋅⋅O distance of 1.72 Å, and with the hydrogen‐acceptor molecule almost freely rotating around its molecular axis. The stretching of the proton donor O–H bond is calculated to be 0.12 Å. A population anaysis near the energy minimum shows that the change in the population is distributed not only in the O⋅⋅⋅H–O fragment, but also delocalized into the neighboring O–H bonds. Hydrogen bonds of dimeric H2O other than the linear structure (cyclic and bifurcated) are also examined.
Article
Ab initio minimal basis LCAOSCF molecular orbital calculations have been performed to determine the energies and configurations of small groups of water molecules, with particular emphasis on those aspects which are relevant to the structure of liquid water. An intermolecular potential which spans the complete range of possible relative orientations for the dimer is presented. The predicted equilibrium form of the dimer is found, together with estimates of some of the intermolecular force constants. Results of calculations on both open and cyclic polymeric water structures containing up to six molecules are included. It is found that polymers having OH⋅⋅⋅OH⋅⋅⋅OH⋅⋅⋅ chains are preferred, and that hydrogen‐bond energies deviate considerably from additivity. Cyclic structures are predicted to be most stable for the trimer and higher polymers.
Article
High‐accuracy molecular orbital calculations have been carried out on different geometries of the hydrogen fluoride dimer and the mixed water–hydrogen fluoride dimer. A zigzag (near linear) structure is predicted for the hydrogen fluoride dimer with a dimerization energy in reasonable agreement with experiment. One geometry of the mixed water–hydrogen fluoride dimer has a very large stabilization energy (10 kcal/mole), and a microwave experiment is proposed to determine its exact structure. Changes in molecular properties and charge distribution upon dimer formation are calculated and a dimer rotational barrier determined.
Article
The radiofrequency and microwave spectra of the K=0 states of (HF)2, (DF)2, and HFDF have been studied by the molecular beam electric resonance method. A unique hydrogen tunnelling motion involving the breaking and reforming of the hydrogen bond causes a splitting of rotational energy levels for (HF)2 and (DF)2, but not for HFDF. The electric dipole selection rules and nuclear spin statistics for the tunnelling molecules have been derived from a consideration of an extended permutation‐inversion group. Rotational constants, tunneling doublings, electric dipole moments, and deuterium quadrupole coupling constants have been determined from the observed spectra of the K=0 states.
Article
This paper presents a survey of recent ab initio SCF calculations on water polymers and examines the relationship between calculated results and the choice of basis set used in the LCAO expansion. It is found that current studies give similar descriptions of the general features of the hydrogen bond, although variations do occur due to the nature and size of the basis set used. In many cases, differences in intermolecular properties can be correlated with differences in the calculated value of the monomer dipole moment.
Article
High‐accuracy molecular‐orbital calculations using essentially Hartree–Fock quality atomic orbitals as a basis have been carried out on different geometries of the water dimer. Different basis sets have been considered. The molecular‐orbital approach is shown to well represent the geometry and heat of formation (− 5.3 kcal/mole) of the water dimer as well as general infrared spectral properties of the hydrogen bond. The individual molecular‐orbital energies are shown to increase for the electron acceptor and to decrease for the electron donor. This trend in energies is proposed as a quantitative organizing principle for not only H‐bond formation but all donor–acceptor interactions.
Article
As a prelude to the study of energy transfer in the HF☒HF system, the potential energy surface for the interaction of two rigid HF molecules has been calculated within the ab initio self‐consistent‐field framework. An H(4s 1p∕2s 1p), F(9s 5p 1d∕4s 2p 1d) basis set of contracted Gaussian function was employed. The number of unique points on the surface is greatly reduced by symmetry, and only 294 points were required to give a fairly complete description of the four‐dimensional surface. Parts of the surface are illustrated by a series of contour maps. Some preliminary attempts to fit the surface to an analytic form are described. The equilibrium geometry of (HF)2 is predicted.
Article
The analytical fit to a large number of Hartree‐Fock computations for the water‐water interaction has been reanalyzed and used to study small clusters of water molecules. With the analytically fitted Hartree‐Fock potential, thousands of possible configurations for the dimers, trimers, tetramers, pentamers, hexamers, heptamers, and octamers of water have been compared in order to determine the configuration of lowest energy (maximal stabilization energy). For the dimer two possible stable configurations are found, corresponding to an open form and a cyclic form, with the open form being more stable. For the trimers and tetramers the cyclic forms are somewhat more stable than the open structures. For the larger clusters it is concluded that it is rather meaningless to consider a single structure, but what is physically relevant is the statistical distribution of different configurations, since many configurations with significantly different geometry have nearly the same energy. The comparison of the stabilization energy per molecule of the different clusters with the corresponding value for liquid water does not support the mixture‐model theories of the structure of liquid water.
Article
Spectra of heavy water have been obtained under high resolution between 1.25—4.1μ (2400—8000 cm—1). Approximately 4500 lines have been measured, and the majority of them analyzed into ten bands of D2O and nine bands of HDO. The analysis is described in some detail, spectra of all bands are shown and a partial table of lines and a complete table of energy levels are presented. The vibration‐rotation constants are derived and compared with those of H2O.
Article
A simple semiempirical method is given for determining the hydrogen bond energy for water clusters in the vapor phase. This method is based on a general statistical‐mechanical theory of clustering. The partition function for a system of clusters is used to determine the equilibrium distribution of clusters. In conjunction with available thermodynamic and spectroscopic data, the cluster equilibrium constants can be used to calculate the cluster potential energy and the hydrogen bond energy. Results for the water dimer agree quite well with other reported values obtained either by quantum‐mechanical calculations or approximate thermodynamic estimates. A correct temperature dependence of the bond energies is found.
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Article
Two experiments using an interferometer and a maser have indicated the occurrence of submillimetre wave absorption by dimeric water. This form of water seems to exist in the Earth's atmosphere.
Article
A physical model of the hydrogen bond, A-H⋯B, has been deduced from ab initio molecular orbital wave functions of 36 dimers made from the monomers, NH3, OH2, FH, PH3, SH2, and ClH. Three monomer quantities are defined which characterize the model: μA-H, the A-H bond dipole; ΔI, the difference between first ionization potentials of the electron donor and the noble gas atom in its row; and l, the length of the hydrogen bonding lone pair. Dimerization energy, charge transfer, internuclear separation, directionality, stretching force constants (KAB and KAH), the dimer dipole moment, and ir intensity enhancement can be understood in terms of these quantities. The dimerization energy formula, ED = KμA-HΔI/R, where K is an energy scale factor and R, the internuclear separation between A and B, systematizes existing experimental and computational data. The tendency for strong bonding electron donors to be weak bonding proton donors and vice versa is the result of an intrinsic reciprocal relationship between μA-H and ΔI. Charge transfer is proportional to μA-H for specified B, and is ordered according to l for a given A. Internuclear separation is inversely proportional to μA-H for specified B, and has close to the same dependence on A-H for second- and third-row electron donors. The almost constant separation difference of 0.8 Å between second- and third-row electron donors results from the difference in average l between the rows. The rule of constant R for all B in a row (with given A) is found to arise from the constancy of l times I. Stretching force constants for the heavy atoms follow Badger's rule, KAB(R - dAB)3 = 1.86, with dAB dependent only on the column of the periodic table. dAB is 1.00, 0.80, and 0.55 Å for groups 5, 6, and 7, respectively. Lowering of the A-H stretching force constant, KAH, relative to the monomer, is proportional to μA-H for fixed B, variable A, and proportional to ΔI (or l) for fixed A, variable B. The model also provides qualitative explanations and some quantitative results for the properties of other hydrogen bonds: the strong hydrogen bonds found in crystal ions, the weak hydrogen bonds to π electrons in organic molecules, the multiply bonded electron donors of proteins, a variety of substituents at A and B, and the cooperativity found in trimers and higher polymers. Quantitative predictions of ED and R can be made for dimers formed with fourth-row hydride monomers.
Article
Hydrogen-bonded dimers involving first- and second-row hydrides have been studied theoretically with ab initio molecular orbital methods, using a 431G basis set. Certain generalizations about H-bonded dimers found in a previous study2a of first-row dimers (those involving NH3, H2O, and HF) are supported by this study; others require modification. In addition to studying the dependence of H-bond energy and properties on the row of the periodic table, we examine the dependence of H-bond energies on the "hybridization" of the electron donor, including HCN, H2CO, H2CS, HNC, and HCP as electron donors. We have also studied ionic H bonds, "π" H bonds, and H-bonded trimers in an attempt to relate their properties to those of the more conventional H-bonded dimers. Can a C-H bond be an effective H-bond proton donor? We attempt to answer this question by examining the proton donor ability of CH4 and CHF3. Electrostatic potentials turn out to facilitate our understanding of H-bond energies and structures, being more useful than Mulliken populations in rationalizing H-bond energies. Finally we address ourselves to the question of predicting dimer H-bond energies from the monomers involved. Using a very simple algebraic model, we are able to predict the H-bond energy of a total 144 H-bonded complexes, using as a basis our theoretical calculations on 25 complexes.
Article
Eine systematische: Untersuchung der Elektronenstruktur der Wasserstoffbrückenbindung in Hydriddimeren der Atome N, O, F, P, Sund Cl wird durchgeführt.
Article
The influence of electron correlation on the linear hydrogen bond in F-H⋯F-H is studied in the frameworks of the IEPA-, CEPA-, and PNO-CI approaches. Due to compensating effects of the intrasystem and the intersystem correlation energy we find a relatively small net effect of the total correlation energy on the interaction energy, the F-F distance, and the intermolecular vibration. The following RFF and ΔE values (in au) result in the SCF-, IEPA-, CEPA-, and PNO-CI approach respectively: 5.48, -0.0055; 5.47, -0.0054; 5.46, -0.0056; 5.43, -0.0056. The intermolecular stretching vibration of the H-F bond involved in the hydrogen bond is hardly affected in comparison with the isolated HF molecule. The experimentally observed shifts of 10-15% in the absorption frequencies of infrared spectra are thus attributed to higher polymers, in agreement with previous theoretical and experimental works.
Article
Ab initio SCF calculations with a minimal STO-3G basis set have been performed on the series of dimers ROH⋯NH3, where R may be H, or one of the isoelectronic substituents CH3, NH2, OH, or F. The equilibrium structures and energies of these dimers are presented and analyzed. The dimer structures are well described in terms of the general hybridization model for the hydrogen bond. While the electrostatic interaction is of primary importance in stabilizing hydrogen bonded dimers, dipole-dipole and long-range interactions are also shown to be important in determining hydrogen bond strengths. Comparisons are made between corresponding dimers in the two series ROH⋯OH2 and ROH⋯NH3.
Article
An ab initio molecular orbital study of the geometries and energies of neutral systems AHn and their singly charged cations AHn+ (A = C, N, O, or F) is presented. Two previously reported basis sets are employed: the minimal, STO-3G, basis and the extended, 4-31G, basis in which valence shells are split into inner and outer parts. Comparisons are made between experimental and theoretically predicted properties.
Article
The Shipman-Scheraga empirical intermolecular potential energy function for water (SS potential) has been applied to a study of the structure, energetics, and dynamics of the water dimer. The entire six-dimensional potential energy surface of the water dimer has been searched for minima and saddle points. Only one minimum-energy structure, the trans near-linear dimer (TNLD), has been found, while several important saddle points that serve as transition states for interconversions between TNLD configurations have been found. The TNLD's of (H2O)2 and (D2O)2 have been characterized by calculating the following properties: potential energy and O ⋯ O distance at the minimum, internal energy at absolute zero temperature, frequencies and dipole moment derivatives of the intermolecular normal vibrational modes, zero-point energy for intermolecular vibrations, principal moments of inertia, location of the center of mass, directions of the principal axes for the moments of inertia, and components of the total dipole moment along the principal axes. The important transition states for intereonversion between the TNLD's have been characterized by calculating the following properties: potential energy, intermolecular vibrational frequencies, intermolecular vibrational zero-point energy, internal energy at absolute zero temperature, and internal energy relative to the TNLD at absolute zero temperature. The familiar cyclic and bifurcated dimers have been found to be saddle points, not minima, on the six-dimensional potential energy surface. The importance of motion through the various transition states for interconversion between the TNLD's has been considered. Implications of the computed results for future spectroscopic studies are discussed.
Article
A model to facilitate the computation of the most stable conformer of associated M H2O (M being a polar molecule) which depends upon the electrostatic interaction energy between the two associated molecules is proposed and tested. SCF electrostatic potentials for the M molecule and a suitable point charge distribution for H2O were employed in the model computations. Energies predicted by the model are found to be in good agreement with those resulting from an ab initio minimal STO basis SCF treatment of some conformations of the H2O dimer.Ein Modell zur Durchfhrung der Berechnung des stabilsten Konformeren eines Assoziationskomplexes M H2O, wobei M ein polares Molekl ist, wird vorgeschlagen und untersucht. Es basiert auf der elektrostatischen Wechselwirkung zwischen beiden Partnern, und zwar wird fr das Molekl M der elektrostatische Anteil seines SCF-Potentials und fr H2O eine angemessene Punktladungsverteilung zugrunde gelegt. Die resultierenden Energien sind in guter bereinstimmung mit denen, die sich bei einer ab initio Rechnung mit minimaler STO Basis ergeben.
Article
The energy of the hydrogen bond N...H-O in the dimer (NH3, H2O) has been computed by the LCAO-MO method, using a minimal set of Slater-type orbitals optimized for the isolated monomers. The doubly occupied and virtual orbitals have been determined by the standard SCF technique, and electron correlation has been introduced by a complete second-order perturbation calculation, using different sets of equivalent MO's. The bonding energy is found to be equal to 7.66 kcal/mol at the SCF step and to 9.65 kcal/mol after second order corrections. The latter value is given by a set of equivalent MO's obtained by projecting the canonical MO's of the monomers into the space of the dimer MO's. The preceding values are reduced to 3.96 kcal/mol at the SCF step and to 4.63 kcal/mol at the second-order, if the basis extension arising from the vicinity of the two monomers inside the dimer is taken into account.