Publications (107)246.47 Total impact
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ABSTRACT: Canonical approaches are applied for investigation of the extraordinarily accurate electronic ground state potentials of H2(+), H2, HeH(+), and LiH using the Virial Theorem. These approaches will be dependent on previous investigations involving the canonical nature of E(R), the BornOppenheimer potential, and F(R), the associated force of E(R), that have been demonstrated to be individually canonical to high accuracy in the case of the systems investigated. Now, the canonical nature of the remaining functions in the Virial Theorem [the electronic kinetic energy T(R), the electrostatic potential energy V(R), and the function W(R) = RF(R)] are investigated and applied to H2, HeH(+), and LiH with H2(+) chosen as reference. The results will be discussed in the context of a different perspective of molecular bonding that goes beyond previous direct applications of the Virial Theorem.  [Show abstract] [Hide abstract]
ABSTRACT: A proofofconcept for the accurate generation of multidimensional intermolecular interaction potentials is demonstrated. The basis for evaluating this application is the available very accurate 3D morphed potential of Ar·HBr. Starting from the welldefined potential of the simplest molecule, the diatomic H2+, a recently developed 1D canonical potential is used with selected 2D polyatomic data to generate the adiabatic intermolecular interaction potential in Ar·HBr, with HBr in the vibrational ground state. This represents the first application of canonical transformations to a higher vibrationally dimensional molecular system, in this case, Ar·HBr. Results indicate intrinsic bonding characteristics inherent to both systems.  [Show abstract] [Hide abstract]
ABSTRACT: Rovibrational transitions associated with tunneling states in the water bending vibration of the atmospherically significant N2–H2O complex have been recorded using a cw supersonic jet quantum cascade laser spectrometer at 6.2 μm. Analysis of the observed spectra is facilitated by incorporating fits of previously recorded microwave and submillimeter data. This accounts for Coriolis coupling to obtain the levels of the ground vibrational state and confirmation of assignment of the excited water bending vibration. The results are used to explore the nature of the associated water bending vibrationally excited states of the complex compared to those in other corresponding water complexes.  [Show abstract] [Hide abstract]
ABSTRACT: A generalized formulation of canonical transformations and spectra are used to investigate the concept of a canonical potential strictly within the BornOppenheimer approximation. Data for the most accurate available ground electronic state pairwise intermolecular potentials in H2, HD, D2, HeH(+), and LiH are used to rigorously evaluate such transformations. The corresponding potentials are generated explicitly using parameters calculated with algebraic functions from that of the single canonical potential of the simplest molecule, H2(+). The efficacy of this approach is further tested by direct comparison of the predicted eigenvalues of all vibrational states in the selected molecular systems considered with the corresponding most accurately known BornOppenheimer eigenvalues currently available. Deviations are demonstrated to be less than 2 cm(1) for all vibrational states in H2, HD, D2, HeH(+), and LiH with an average standard deviation of 0.27 cm(1) for the 87 states considered. The implications of these results for molecular quantum chemistry will be discussed. 
Article: A General Transformation to Canonical Form for Potentials in Pairwise Interatomic Interactions
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ABSTRACT: A generalized formulation of explicit forcebased transformations is introduced to investigate the concept of a canonical potential in both fundamental chemical and intermolecular bonding. Different classes of representative ground electronic state pairwise interatomic interactions are referenced to a chosen canonical potential illustrating application of such transformations. Specifically, accurately determined potentials of the diatomic molecules H2, H2+, HF, LiH, argon dimer, and onedimensional dissociative coordinates in ArHBr, OCHF, and OCCl2 are investigated throughout their bound potentials. Advantages of the current formulation for accurately evaluating equilibrium dissociation energies and a fundamentally different unified perspective on nature of intermolecular interactions will be emphasized. In particular, this canonical approach has significance to previous assertions that there is no very fundamental distinction between van der Waals bonding and covalent bonding or for that matter hydrogen and halogen bonds.  [Show abstract] [Hide abstract]
ABSTRACT: The ν1 spectra of 16O12CDI and 16O12CID, as well as ν2 of 16O12CDI, 16O12CID have been recorded using a quantum cascade laser pulsed slit supersonic jet spectrometer. Intensity measurements made simultaneously in the same expansion for transitions in ν2 16O12CHI: 16O12CIH and ν1 16O12CDI: 16O12CID isomers permit determination of the isomerization for the former pair to be +2.8(1.0) and the latter −6.0(1.0) cm−1. These results confirm prediction of ground state deuterium isotopic isomerization made using a generated morphed potential. Further analyses indicate OC.HI is a prototype for complexities associated with isomerization and isotopic effects in excited stretching vibrations.  [Show abstract] [Hide abstract]
ABSTRACT: Different classes of ground electronic state pairwise interatomic interactions are referenced to a single canonical potential using explicit transformations. These approaches have been applied to diatomic molecules N2, CO, H2(+), H2, HF, LiH, Mg2, Ca2, O2; argon dimer, and onedimensional cuts through multidimensional potentials of OCHBr, OCHF, OCHCCH, OCHCN, OCHCl, OCHI, OCBrCl, and OCCl2 using accurate semiempirically determined interatomic RydbergKleinRees (RKR) and morphed intermolecular potentials. These different bonding categories are represented in these systems which vary from van der Waals, halogen bonding, hydrogen bonding to strongly bound covalent molecules with binding energies covering three orders of magnitude from 84.5 cm(1) to 89600.6 cm(1) in ground state dissociation energies. Such approaches were then utilized to give a unified perspective on the nature of bonding in the whole range of diatomic and intermolecular interactions investigated.  [Show abstract] [Hide abstract]
ABSTRACT: A fivedimensional compoundmodel morphed (CMM) potential has been generated for the halogen bonded intermolecular interaction 16O12C79Br35Cl based on a fit to the currently generated infrared and previously available microwave spectroscopic data. The experimentally determined blue frequency shift of the 16O12C stretching frequency on complexation with 79Br35Cl is found to be Δν = 12.89643(28) cm1 indicating a more strongly bound complex than in OC35Cl2. Re centerofmass to centerofmass distance of 4.270(7) Å and dissociation energies De = 778(70) cm1 and D0 = 605(70) cm1 are predicted from the CMM potential and also compared with the corresponding values of Re = 4.742(3) Å and De = 544(5) cm1 and D0 = 397(5) cm1 for 16O12C35Cl2. The molecular dynamics, binding energy and other molecular parameters of OCBrCl are also compared with the hydrogen bonded dimers OCHX (X = F, Cl, Br) giving further insight into the characteristics of the complex.  [Show abstract] [Hide abstract]
ABSTRACT: Potential morphing has been applied to the investigation of proper blue frequency shifts, Δν0 in CO, the hydrogen acceptor complexing in the hydrogen bonded series OCHX (X=F, Cl, Br, I, CN, CCH). Linear correlations of morphed hydrogen bonded ground dissociation energies D0 with experimentally determined Δν0 free from matrix and solvent effects demonstrate consistency with original tenets of the BadgerBauer rule [J. Chem. Phys. 5, 83951(1937)]. A model is developed that provides a basis for explaining the observed linear correlations in the range of systems studied. Furthermore, the generated calibration curve enables prediction of dissociation energies for other related but different complexes. The latter include D0 for H2OCO, H2SCO and OCHOCH3 which are predicted by interpolation and found to be 355(13), 171(11) and 377(14) cm(1) respectively from available experimentally determined proton acceptor shifts. Results from this study will also be discussed in relation to investigations in which CO has been used as a probe of heme protein active sites.  [Show abstract] [Hide abstract]
ABSTRACT: Rovibrational manifolds in low frequency intermolecular vibrations of prototypical hydrogenbonded interactions OC–HX (X = F, Cl, CN) are reported using a near infrared quantum cascade cw supersonic jet spectrometer. (i) OC–HCl is studied to evaluate future capabilities of the QCL spectrometer. (ii) Analysis of OC–HF demonstrates applicability to vibrations greater than 80 cm−1 above the ground state. ν51 band origins in OC–1H35Cl and OC–1H19F are 48.9944(2) and 81.96825(12) cm−1 respectively. (iii) The corresponding intermolecular ν71 band origin of OC–HCN is 34.63742(18) cm−1 and its corresponding rovibrational spectrum made available for attempted detection in interstellar space. Analysis of ν2, ν2+ν71ν71, ν2+ν71, and ν2+ν61 vibrations in OC–HCN also enables generation of its 5dimensional semiempirical intermolecular potential. Structural and other properties of OC–HCN are then compared with corresponding properties predicted using morphed potentials for the homologous series OC–HX (X = F, Cl, Br, I). These results permit investigation of blue shifts in OC vibrations for this homologous series.  [Show abstract] [Hide abstract]
ABSTRACT: A recently generated sixdimensional vibrationallycomplete compoundmodel morphed (CMMRS) potential for the pairwise interaction between OC and HF is used to predict spectroscopic and other properties of the isomer CO–HF. The equilibrium dissociation energy and internuclear diatomic centerofmass centerofmass distances are evaluated respectively as De = 643(10) cm−1 and Re = 3.442(2) Å with an energy difference ΔE between the OC–HF and CO–HF minima in the potential energy surface of 667(10) cm−1. The CO–HF isomer is also predicted to have a local minimum state with dissociation energy D0 = 310.5(50) cm−1 which corresponds to 432(10) cm−1 above the ground state of OC–HF. Band origins for its fundamental vibrations are predicted to be: ν1 = 3938.85(100) cm−1, ν2 = 2134.52(100) cm−1, ν3 = 80.56(100) cm−1, ν41 = 205.65(100) cm−1, and ν51 = 39.55(100) cm−1 and can be compared with currently available data from matrix isolation and other spectroscopic techniques. Such predictions will also facilitate future gas phase spectroscopic investigations of the CO–HF isomeric species and ultimately critical evaluation of the predictive capabilities of the available CMMRS potential as well as those of previously published ab initio potentials.  [Show abstract] [Hide abstract]
ABSTRACT: Spectroscopic studies of the OC:HCCH complex are reported using a continuous supersonic slit jet spectrometer with broadband frequency modehop free tunable infrared quantum cascade lasers (QCL), centered at 4.4 and 4.6 μm. This Letter includes an extended analysis of the ν3 CO stretching vibration frequency, and investigation of the ν3 + ν91 − ν91 hot band, the ν3 + ν91 and ν3 + ν81 combination bands for OC–HCCH. The ground state low frequency bend, ν91, is determined at 20.48361(20) cm−1. The generated rovibrational data is incorporated with previously determined information and used to generate a fourdimensional compoundmodel morphed potential with radial correction, giving further insight into the molecular dynamics of this complex.  [Show abstract] [Hide abstract]
ABSTRACT: Transitions associated with the vibrations ν₁, ν₁ + ν(b)¹, ν₁ + ν₅¹, and ν₁ + ν₅¹  ν₅¹ of the complex OC···Cl₂ have been rovibrationally analyzed for several isotopologues involving isotopic substitutions in Cl₂. Spectra were recorded using a recently constructed nearinfrared (4.34 to 4.56 μm), quantumcascade laser spectrometer with cw supersonic slit jet expansion. Spectral analysis allowed precise determination of the ν₅¹ intermolecular vibration of OC³⁵Cl₂ to be 25.977637(80) cm⁻¹. These results were incorporated with other previously determined data into a spectroscopic database for generation of a fivedimensional morphed potential energy surface. This compoundmodel morphed potential with radial shifting (CMMRS) was then used to make more accurate predictions of properties of the OC³⁵Cl₂ complex including D(e) = 544(5) cm⁻¹, D₀ = 397(5) cm⁻¹, ν₃ = 56.43(4) cm⁻¹, and ν(b)¹ = 85.43(4) cm⁻¹. The CMMRS potential determined for OCCl₂ was also used to compare quantitatively many of the inherent properties of this noncovalent halogen bonded complex with those of the closely related hydrogenbonded complex OCHCl, which has a similar dissociation energy D₀. We found that in the ground state, the CO bending amplitude is larger in OCCl₂ than in OCHCl.  [Show abstract] [Hide abstract]
ABSTRACT: A 6dimensional vibrationallycomplete compoundmodel morphed potential with radial shifting (CMMRS) has been generated for the hydrogenbonded dimer OC–HF. Four morphing parameters only are optimized correcting for inadequacies in the underlying ab initio potential. The morphing transformation utilized a rotationally resolved spectroscopic database composed of microwave and near infrared spectroscopic information. Band origin vibrational frequencies are fitted to an average standard deviation of 0.016cm−1. The equilibrium rotational constant of OC–HF is determined to be Be=3345.68(30)MHz, equilibrium center of mass CO to center of mass HF distance, Re=3.598(1)Å, and equilibrium dissociation energy De=1310(10)cm−1. Ground state dissociation energy D0=742.5(50)cm−1, first order anharmonic constants and other properties of the complex are also evaluated. Characteristics of the CMMRS potential can also be compared with predictions using previous ab initio potentials. Limitations of the morphing methodology and its potential applications are also discussed.  [Show abstract] [Hide abstract]
ABSTRACT: Application of tunable infrared lasers to the spectroscopic investigation of equilibrium, gaseous hydrogenbonded systems is demonstrated. Broadband spectra of the nν6 + ν1 − nν6 vibrations in and have been recorded with a computercontrolled multimode color center laser using both conventional absorption and infraredacoustic detection methods.  [Show abstract] [Hide abstract]
ABSTRACT: A broadband v3 subDoppler spectrum of HCN has been recorded in the range 3340–3280 cm−1 using a single frequency continuously scanable computercontrolled color center laser optothermal molecular beam spectrometer. Absolute frequencies for rovibrational transitions R(9) through P(9) have been determined to an accuracy ≤ 20 MHz or 2 parts in 107. An unconstrained fiveparameter fit to this datum results in molecular constants: B″ = 1.47822146(182), D″ = 2.881(23) × 10−6, B′ = 1.46779974(154), D′ = 2.863(18) × 10−6, and v0 = 3311.47758(2) cm−1, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: The HI homodimer was found to have structural and vibrational properties unlike any other previously studied (HX)2 system, with X F, Cl, and Br. The infrared spectrum of (HI)2 is also observed to be distinctly different from the other members of the series. In addition, the interaction energy of the (HI)2 dimer has been calculated using the coupledcluster with singles, doubles, and perturbative triples [CCSD(T)] level of theory. A fourdimensional morphed intermolecular potential has been generated and then morphed using available near infrared and submillimeter spectroscopic data recorded in supersonic jet expansions. The morphed potential is found to have a single global minimum with a symmetric structure having C2h symmetry. The equilibrium dissociation energy is found to be 359 cm1 with the geometry in Jacobi coordinates of Re 4.35 , 1 43, 2 137, and 180. The infrared spectrum is characterized by pairs of excited vibrational states resulting from the coupling of the two HI stretching modes. A qualitative model using a quadratic approximation has been fitted to obtain an estimate of this coupling. Furthermore, a morphed intermolecular potential for the vibrationally excited system was also obtained that gives a quantitative estimate of the shift in the potential due to the excitation. The submillimeter analysis is consistent with a ground state having its highest probability as a paired hydrogen bond configuration with R0 4.56372(1) and an average angle =cos1(cos 21/2) 46.40(1) (between the diatom center of masscenter of mass axis and direction of each component hydrogen iodide molecule). On monodeuteration, however, the ground state is predicted to undergo an anomalous structural isotope change to an Lshaped HIDI structure with highest probability at R 0 4.51, 183, 2177, and 180. These results provide a test for large scale ab initio calculations and have implications for the interpretation of photoinduced chemistry and other properties of the dimer.  [Show abstract] [Hide abstract]
ABSTRACT: Design and testing of a THz sensor ultimately to be capable of operating from 0.068 to 8.1 THz are presented. Results for modular approaches in the mm and submm spectral regions are reported utilizing cavityenhanced techniques. Investigations indicate ppq levels of detection for molecular species with 1.0 Debyes dipole moment. 
Article: Infrared quantum cascade laser spectroscopy of low frequency vibrations of intermolecular complexes
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ABSTRACT: Application of a QCL based spectrometer to cw supersonic slit jet expansions of CO and HX (X= F, Cl, CN, CCH) are reported. Spectroscopic analysis of fundamental, combination and hot bands of the CO stretching vibrations provide rovibrational parameters for low frequency intermolecular vibrations that can be incorporated in determination of morphed potentials for the respective dimers.  [Show abstract] [Hide abstract]
ABSTRACT: An extended analysis of the noncovalent interaction OC:HI is reported using microwave and infrared supersonic jet spectroscopic techniques. All available spectroscopic data then provide the basis for generating an accurately determined vibrationally complete semiempirical intermolecular potential function using a fourdimensional potential coordinate morphing methodology. These results are consistent with the existence of four bound isomers: OCHI, OCIH, COHI, and COIH. Analysis also leads to unequivocal characterization of the common isotopic ground state as having the OCHI structure and with the first excited state having the OCIH structure with an energy of 3.4683(80) cm(1) above the ground state. The potential is consistent with the following barriers between the pairs of isomers: 382(4) cm(1) (OCIH/OCHI), 294(5) cm(1) (COIH/COHI), 324(3) cm(1) (OCIH/COIH), and 301(2) cm(1) (OCHI/COHI) defined with respect to each lower minimum. The potential is also determined to have a linear OCIH van der Waals global equilibrium minimum structure having R(e)=4.180(11) Å, θ(1)=0.00(1)°, and θ(2)=0.00(1)°. This is differentiated from its OCHI ground state hydrogen bound structure having R(0)=4.895(1) Å, θ(1)=20.48(1)°, and θ(2)=155.213(1)° where the distances are defined between the centers of mass of the monomers and θ(1) and θ(2) as cos(1)[<cos(2) θ(i)>(1/2)] for i=1 and 2. A fundamentally new molecular phenomenon  ground state isotopic isomerization is proposed based on the generated semiempirical potential. The protonated ground state hydrogenbonded OCHI structure is predicted to be converted on deuteration to the corresponding ground state van der Waals OCID isomeric structure. This results in a large anomalous isotope effect in which the R(0) center of mass distance between monomeric components changes from 4.895(1) to 4.286(1) Å. Such a proposed isotopic effect is demonstrated to be a consequence of differential zero point energy factors resulting from the shallower nature of hydrogen bonding at a local potential minimum (greater quartic character of the potential) relative to the corresponding van der Waals global minimum. Further consequences of this anomalous deuterium isotope effect are also discussed.
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1k  Citations  
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Institutions

19822015

Texas A&M University
 Department of Chemistry
College Station, Texas, United States


19972004

Alabama A & M University
Huntsville, Alabama, United States


1996

Université de Montréal
 Department of Physics
Montréal, Quebec, Canada


19921993

University of Exeter
 Department of Biosciences
Exeter, England, United Kingdom
