The Journal of Physical Chemistry A (J Phys Chem)

Publications in this journal

• Article: Formation of Core-Shell Silver-Ethane Clusters in He Droplets.

  Evgeny Loginov, Luis F Gomez, Andrey F Vilesov
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  ABSTRACT: Here we study the utility of large helium droplets of 10(5)-10(7) atoms for the growth of composite clusters consisting of a silver core and a shell of ethane molecules. The clusters have been assembled by doping He droplets with up to 10(3) silver atoms and ethane molecules in two sequential pickup cells and studied via infrared spectroscopy in the C-H stretch region of the ethane molecules. We found that the ν7 band of ethane molecules on the interface with the silver atoms has a low frequency shift of approximately 15 cm(-1) with respect to that of more distant ethane molecules away from the interface. The intensity ratio of the two bands was used for evaluation of the Ag core and ethane shell cluster structure. We found that the number of surface ethane molecules is in good agreement with a model which takes dense core-shell clusters for clusters containing less than about 100 atoms. However, large Ag clusters consisting of about 3000 atoms have a factor of about 5 larger surface area than predicted by the model, indicating a ramified structure for such larger Ag clusters obtained in liquid helium. Moreover, we demonstrate that helium droplets behave as calorimeters for measurements of the number of captured atoms and molecules as well as the amount of absorbed laser energy.
  The Journal of Physical Chemistry A 06/2013;
• Article: Probing the Smallest Molecular Model of MoS2 Catalyst: S2 Units in the MoSn(-/0) (n = 1 - 5) Clusters.

  Bin Wang, Ni Wu, Xiao-Bin Zhang, Xin Huang, Yong-Fan Zhang, Wen-Kai Chen, Kai-Ning Ding
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  ABSTRACT: Density functional theory (DFT) calculations are carried out to investigate the electronic and structural properties of a series of mono-molybdenum sulfide clusters, MoSn-/0 (n = 1-5). Generalized Koopmans' theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra (PES). We found that the additional sulfur atoms have a tendency to successively occupy the terminal sites in the sequential sulfidation until the Mo reaches its maximum oxidation sate of +6. After that, the polysulfide ligands (viz., S2 and S3) emerge in the MoS4 and MoS5-/0 clusters. The MoS4 (C2, 1A) is predicted to be the ground state and may be used as a neutral model for the sulfur-rich edge sites of the fresh MoS2 catalysts. Molecular orbital analyses are performed to analyze the chemical bonding in the mono-molybdenum sulfide clusters and to elucidate their electronic and structural evolution.
  The Journal of Physical Chemistry A 06/2013;
• Article: Time-Resolved EPR Study of Singlet Oxygen in the Gas Phase.

  Marco Ruzzi, Elena Sartori, Alberto Moscatelli, Igor V Khudyakov, Nicholas J Turro
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  ABSTRACT: X-band EPR spectra of singlet O2((1)Δg) and triplet O2((3)Σg(-)) were observed in the gas phase under low molecular-oxygen pressures PO2 = 0.175-0.625 Torr, T = 293-323 K. O2((1)Δg) was produced by quenching of photogenerated triplet sensitizers naphthalene C8H10, perdeuterated naphthalene, and perfluoronaphthalene in the gas phase. The EPR spectrum of O2((1)Δg) was also observed under microwave discharge. Integrated intensities and line widths of individual components of the EPR spectrum of O2((3)Σg(-)) were used as internal standards for estimating the concentration of O2 species and PO2 in the EPR cavity. Time-resolved (TR) EPR experiments of C8H10 were the main focus of this Article. Pulsed irradiation of C8H10 in the presence of O2((3)Σg(-)) allowed us to determine the kinetics of formation and decay for each of the four components of the O2((1)Δg) EPR signal, which lasted for only a few seconds. We found that the kinetics of EPR-component decay fit nicely to a biexponential kinetics law. The TR EPR 2D spectrum of the third component of the O2((1)Δg) EPR spectrum was examined in experiments using C8H10. This spectrum vividly presents the time evolution of an EPR component. The largest EPR signal and the longest lifetime of O2((1)Δg), τ = 0.4 s, were observed at medium pressure PO2 = 0.4 Torr, T = 293 K. The mechanism of O2((1)Δg) decay in the presence of photosensitizers is discussed. EPR spectra of O2((1)Δg) evidence that the spin-rotational states of O2((1)Δg) are populated according to Boltzmann distribution in the studied time range of 10-100 ms. We believe that this is the first report dealing with the dependence of O2((1)Δg) EPR line width on PO2 and T.
  The Journal of Physical Chemistry A 06/2013;
• Article: Electronic Properties of RDX and HMX: Compton Scattering Experiment and First-Principle Calculation.

  B L Ahuja, Pradeep Jain, Jagrati Sahariya, N L Heda, Pramod Soni
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  ABSTRACT: The first-ever electron momentum density (EMD) measurements of explosive materials namely RDX and HMX have been reported using 740 GBq 137Cs Compton spectrometer. Experimental Compton profiles (CPs) are compared with the EMDs derived from linear combination of atomic orbitals with density functional theory. It is found that the CPs deduced from generalized gradient approximation (GGA) with Wu-Cohen exchange energies give a better agreement with the corresponding experimental profiles than those from local density approximation and other schemes of GGA. Further, Mulliken population, energy bands, partial and total density of states and band gap have also been reported using GGA calculations. Present ground state calculations unambiguously show large band gap semi-conductor nature of both RDX and HMX. Similar type of bonding in these materials is uniquely established using Compton data and density of states. It is also outstandingly consistent with the Mulliken population which predict almost equal amount of charge transfer (0.84 and 0.83 e-) from H1+H2+N2 to C1+N1+O1+O2 in both the explosives.
  The Journal of Physical Chemistry A 06/2013;
• Article: Formation of Indium Carbide Cluster Ions: Experimental and Computational Study.

  Jonathan Bernstein, Eran Armon, Erez Zemel, Eli Kolodney
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  ABSTRACT: We report the detection and structural analysis of novel indium carbide gas phase cluster ions generated by bombardment of a clean indium surface by keV C60- ions. Positive InmCn+ (m = 1-21, 1 ≤ n ≤ 9) ions were ejected off the surface and analyzed mass spectrometrically. C60- ion beam irradiation is shown to be an efficient way of producing new kinds of gas phase carbide ions with relatively balanced stoichiometries. The rise kinetics of the ion signal (immediate jump within the beam opening time to a plateau value) indicates that the formation/ejection of the carbide ions constitute a single impact event. In3C2+ was found to be the most abundant carbide cluster ion. Optimal geometries of the different clusters were derived via density functional theory calculations. The acetylenic/cumulenic nature of the impact emitted cluster ions is manifested by the high abundance of In2C2+, In3C2+ and the calculated structures for InmCn+ (m=3-4, n=2-8). Odd/even intensity alternations in the In3Cn+ (n=1-8) and In4Cn+ (n=1-9) abundances are observed and rationalized by the calculations.
  The Journal of Physical Chemistry A 06/2013;
• Article: C-Cl Activation by Group IV Metal Oxides in Solid Argon Matrices: Matrix Isolation Infrared Spectroscopy and Theoretical calculations Investigations of the Reactions of MOx(Ti, Zr; x=1, 2) with CH3Cl.

  Yanying Zhao
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  ABSTRACT: Reactions of the ground state titanium and zirconium monoxide and dioxide molecules with monochloromethane in excess argon matrices have been investigated in solid argon by infrared absorption spectroscopy and density functional theoretical calculations. The results show that the ground state MOx (M=Ti, Zr; x=1, 2) molecules react with CH3Cl to firstly form the weakly bound MO(CH3Cl) and MO2(CH3Cl) complexes. The MO(CH3Cl) complexes can rearrange to the CH3M(O)Cl isomers with the Cl atom of CH3Cl coordination to the metal center of MO upon UV light irradiation (λ< 300 nm). Theoretical calculations indicate the electronic state crossings exist from the MO+CH3Cl reaction to the more stable CH3M(O)Cl molecules via the MO(CH3Cl) complexes traverse their corresponding transition states. The MO2(CH3Cl) complexes can isomerize to the more stable CH3OM(O)Cl molecules with the addition of the C-Cl bond of CH3Cl to one of the O=M bond of MO2 on annealing after broad band light irradiation. The C-Cl activation by MOx mechanism were interpreted by the calculated potential energy profiles.
  The Journal of Physical Chemistry A 06/2013;
• Article: Benchmark Study of the Interaction Energy of a (H2O)16 Cluster: Quantum Monte Carlo and Complete Basis Set Limit MP2 Results.

  Fangfang Wang, Michael Deible, Kenneth D Jordan
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  ABSTRACT: The quantum Monte Carlo method is used to calculate the binding energy of an (H2O)16 cluster that has been the subject of several recent theoretical studies. The resulting interaction energy, -165.1(8) kcal/mol, is very close to our MP2 complete basis set limit interaction energy of -164.1 kcal/mol. Comparison of these results with those from values of the one-, two-, three-, and four-body interaction energies leads us to conclude that the five- and higher-body interactions are attractive, contributing over 2 kcal/mol to the net interaction energy of the (H2O)16 isomer.
  The Journal of Physical Chemistry A 06/2013;
• Article: Thermal Lattice Expansion Effect on Reactive Scattering of H2 from Cu(111) at Ts = 925 K.

  Arobendo Mondal, Mark Wijzenbroek, Matteo Bonfanti, Cristina Diaz, Geert-Jan Kroes
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  ABSTRACT: Surface phonons and surface temperature may have important effects on reactions of molecules at surfaces, and at present much remains unknown about these effects. A question addressed here, which has received little attention so far, is how reaction at elevated temperature is affected by thermal lattice expansion. To answer this question for the benchmark reaction of H2 and D2 with Cu(111) we have performed quantum and quasi-classical dynamics calculations. The specific reaction parameter (SRP) approach to density functional theory (DFT) has been used to compute the required six-dimensional potential energy surfaces (PES). Computed reaction probabilities and rotational quadrupole alignment parameters have been compared for surface temperatures Ts = 0 K and 925 K. Surface thermal expansion of the lattice leads to a considerable decrease of reaction barrier heights, and thereby to increased reaction probabilities as well as decreased rotational quadrupole alignment parameter values in associative desorption.
  The Journal of Physical Chemistry A 06/2013;
• Article: Ab Initio Potential Energy Curves for the Ground and Low Lying Excited States of NH- and the Effect of (2)∑(±) States on Λ-Doubling of the Ground State X(2)Π

  Saurabh Srivastava, Naraya Sathyamurthy
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  ABSTRACT: Complete basis set extrapolated ab initio potential energy curves obtained from multi-reference configuration interaction (MRCI) level calculations for the ground state (X(2)Π) and the a(4)Σ- state of NH- and the ground state (X(3)Σ-) of NH are reported. The potential energy curves for the A'(2)Σ- and A(2)Σ+ states of NH- have been computed using the V6Z basis set at the MRCI level. Λ-doubling parameters p and q are calculated for the ground and the first excited vibrational states of the ground electronic state of NH- using second order perturbation theory. The effect of the (2)Σ+ and (2)Σ- states on the Λ-doubling values is discussed. Earlier experiments had not considered the influence of the (2)Σ- state on p and q while fitting the spectral data. Using the computed potential energy curves and the ro-vibrational spectra including the fine splitting, the threshold for electron detachment has been computed. The result is in agreement with the experimental values of Neumark et al.[J. Chem. Phys. 83, 4364 (1985)] and Farley et al.[Phys. Rev. A, 35, 1099 (1987)].
  The Journal of Physical Chemistry A 06/2013;
• Article: On the Effect of Roaming Transition States Upon Product Branching in the Thermal Decomposition of CH3NO2.

  Rongshun Zhu, Raghunath Putikam, Ming-Chang Lin
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  ABSTRACT: The kinetics for the thermal unimolecular decomposition of CH3NO2 and its structural isomer CH3ONO have been investigated by statistical theory calculations based on the potential energy surface calculated at the UCCSD(T)/CBS and CASPT3(8, 8)/6-311+G(3df, 2p) levels. Our results show that for the decomposition of CH3NO2 at pressures less than 2 Torr, isomerization to CH3ONO via the recently located roaming transition state is dominant in the entire temperature range studied, 400 ~ 3000 K. However, at higher pressures, the formation of the commonly assumed products, CH3 + NO2, becomes competitive and at pressures higher than 200 Torr the production of CH3 + NO2 is exclusive. The predicted rate constants for 760 Torr and the high-pressure limit with Ar as diluent in the temperature range of 500 - 3000 K, which represents solely for CH3 + NO2 production, can be expressed respectively by: k(760)d (CH3NO2) = 2.939 × 10(55) T(-12.6) exp (-35,500/T) s(-1); k(∞)d(CH3NO2) = 5.88 × 10(24) T (-2.35) exp (-31,400/T) s(-1). In the low pressure limit, the decomposition reaction takes place exclusively via the roaming TS producing internally excited CH3ONO, giving rise to both CH3O + NO and CH3O + HNO with the second order rate constant, k(0)d(CH3NO2) = 1.17× 10(31)T(-10.94) exp (-32,400/T)cm(3)molecule(-1)s(-1). For CH3ONO decomposition, a new roaming transition state connecting to the CH2O + HNO products has been located, lying 6.8 kcal/mol below the well-known four-member ring tight transition state and 0.7 kcal/mol below CH3O + NO. The rate constants predicted by similar calculations give rise to the following expressions for the thermal decomposition of CH3ONO in He: k(760)d(CH3ONO) = 8.745×10(41) T(-8.97)exp (-22,600/T) s(-1), kd(0)(CH3ONO) = 8.91×10(19)T(-7.92) exp (-22, 300/T) cm(3)molecule(-1)s(-1) and kd(∞)( CH3ONO) = 1.58 × 10(23) T(-2.18) exp (-21,100/T) s(-1) in the temperature range of 300 - 3000 K. These results are in very good agreement with available experimental data obtained under practical pressure conditions. The much different branching ratios for the formation of CH3O + NO and CH2O + HNO in the decomposition of both CH3NO2 and CH3ONO are also given in this work.
  The Journal of Physical Chemistry A 06/2013;
• Article: Freezing of Heavy Water (D2O) Nanodroplets.

  Ashutosh Bhabhe, Harshad Pathak, Barbara E Wyslouzil
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  ABSTRACT: We follow the freezing of heavy water (D2O) nanodroplets formed in a supersonic nozzle apparatus using position resolved pressure trace measurements, Fourier transform infra-red spectroscopy and small angle X-ray scattering. For these 3 nm to 9 nm radii droplets, freezing starts between 223 K and 225 K, at volume based ice nucleation rates Jice,V on the order of 10^23 cm-3s-1 or surface based ice nucleation rates Jice,S on the order of 10^16 cm-2s-1. The temperatures corresponding to the onset of D2O ice nucleation are higher than those reported for H2O by Manka et al. [A. Manka, H. Pathak, S. Tanimura, J. Wölk, R. Strey and B. Wyslouzil, Phys. Chem. Chem. Phys., 14, 4505, (2012)]. Although the values of Jice,S scale somewhat better with droplet size than values of Jice,V, the data are not accurate enough to state that nucleation is surface initiated. Finally, using current estimates of the thermophysical properties of D2O and the theoretical framework presented by Murray et al. [B. J. Murray, S. L. Broadley, T. W. Wilson, S. J. Bull, R. H. Wills, H. K. Christenson and E. J. Murray, Phys. Chem. Chem. Phys. 12, 10380 (2010)], we find that the theoretical ice nucleation rates are within 3 orders of magnitude of the measured rates over a ~15 K temperature range.
  The Journal of Physical Chemistry A 06/2013;
• Article: The Conformational Transferability of the Sulfenyl Carbonyl Group -SC(O)- in Cyclic Thioesters.

  Nahir Y Dugarte, Mauricio Federico Erben, Evamarie Hey-Hawkins, Peter Lönnecke, Sven Stadlbauer, Maofa Ge, Yao Li, Oscar E Piro, Gustavo A Echeverría, Carlos Omar Della Védova
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  ABSTRACT: The molecular and crystal structures of two di-thiolactones (formally dimers of ε-caprothiolactone and ω-hexadecathiolactone) have been determined by X-ray diffraction at low temperature, revealing that the thioester group is planar with a synperiplanar orientation of the C=O double bond with respect to the S-C single bond. This conformational behavior is in contrast to that found for the smaller cyclic members of this family, where the antiperiplanar conformation is enforced. It is hypothesized that strain effects play a major role for the energy balance in the conformational preference. In this context, the molecular, vibrational (infrared and Raman) and electronic properties of ε-caprothiolactone have also been analyzed by using a combined experimental - including gas phase helium I photoelectron spectroscopy - and computational approach.
  The Journal of Physical Chemistry A 06/2013;
• Article: Influence of Substituent Type and Position on the Adsorption Mechanism of Phenylboronic Acids: Infrared, Raman, and Surface-Enhanced Raman Spectroscopy Studies.

  Natalia Piergies, Edyta Proniewicz, Yukihiro Ozaki, Younkyoo Kim, Leonard M Proniewicz
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  ABSTRACT: This paper shows systematic spectroscopic studies using Fourier-transform infrared absorption (FT-IR), Fourier-transform Raman (FT-Raman), and surface enhanced Raman (SERS) in an aqueous silver sol of fluoro- and formyl- analogues of phenylboronic acids: 2-fluorophenylboronic acid (2-F-PhB(OH)2), 3-fluorophenylboronic acid (3-F-PhB(OH)2), 4-fluorophenylboronic acid (4-F-PhB(OH)2), 2-formylphenylboronic acid (2-CHO-PhB(OH)2), 3-formylphenylboronic acid (3-CHO-PhB(OH)2), and 4-formylphenylboronic acid (4-CHO-PhB(OH)2). To produce an extensive look-up table of vibrational spectra, Density Functional Theory (DFT) calculations with the B3LYP method at the 6-311 ++ G(d,p) level of theory were performed for the ground state geometry of the most stable species - dimers in cis-trans conformation. Based on the SERS spectral profile, the adsorption modes of the phenylboronic acid isomers were proposed. The type of substituent and its position in the phenyl ring have a strong influence on the geometry of isomers on the silver nanoparticle's surface. This effect was especially evident in the case of 4-CH-PhB(OH)2, for which dearomatization of the phenyl ring took place upon adsorption.
  The Journal of Physical Chemistry A 06/2013;
• Article: Indirect Rotational Spectroscopy of HCO+

  Brian M Siller, James N Hodges, Adam J Perry, Benjamin J McCall
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  ABSTRACT: Spectroscopy of the nu1 band of the astrophysically relevant ion HCO+ is performed with an optical parametric oscillator calibrated with an optical frequency comb. The sub-MHz accuracy of this technique was confirmed by performing a combination differences analysis with the acquired rovibrational data and comparing the results to known ground-state rotational transitions. A similar combination differences analysis was performed from the same data set to calculate the previously unobserved rotational spectrum of the nu1 vibrationally excited state with precision sufficient for astronomical detection. Initial results of cavity-enhanced sub-Doppler spectroscopy are also presented, and hold promise for further improving the accuracy and precision in the near future.
  The Journal of Physical Chemistry A 06/2013;
• Article: Solvent Induced Shifts in the UV Spectrum of Amides.

  Nuwan Desilva, Soohaeng Y Willow, Mark S Gordon
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  ABSTRACT: Solvent effects on the electronic spectra of formamide and trans-N-methylacetamide are studied using four different levels of theory: singly excited configuration interaction (CIS), equations of motion coupled-cluster theory with singles and doubles (EOM-CCSD), completely renormalized coupled-cluster theory with singles and doubles with perturbative triple excitations (CR-EOM-CCSD(T)), and time dependent density functional theory (TDDFT), employing small clusters of water molecules. The solvent effects are further simulated using 100 waters modeled with the effective fragment potential method. The simulated electronic spectrum exhibits a blue-shift and red-shift, respectively, for the n→π* and πnb→π* vertical excitation energies, in good agreement with the experimental electronic spectra of amides.
  The Journal of Physical Chemistry A 06/2013;
• Article: Solvent Effect on Thermally Activated Delayed Fluorescence by 1,2,3,5-Tetrakis(carbazol-9-yl)-4,6-dicyanobenzene.

  Ryoichi Ishimatsu, Shigeyuki Matsunami, Katsuyuki Shizu, Chihaya Adachi, Koji Nakano, Toshihiko Imato
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  ABSTRACT: Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T1) to the singlet excited state (S1), where these states are separated by a small energy gap (Est), followed by a radiative transition to the ground state (S0). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol and acetonitrile). We revealed that the rate constant of RISC, kRISC, which is the most important factor for TADF, was significantly enhanced by a reduced Est in more polar solvents. The smaller Est was mainly attributable to a stabilization of the S1 state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S1 and S0 states (17 D). Despite of this factor, we observed a negative correlation between Est and efficiency of the delayed fluorescence (d). This was ascribed to a lower intersystem crossing rate, kISC, and increased non-radiative decay from S1, k_nr^s, in polar solvents.
  The Journal of Physical Chemistry A 06/2013;
• Article: The Mobility of Supercooled Liquid Toluene, Ethylbenzene, and Benzene near Their Glass Transition Temperatures Investigated Using Inert Gas Permeation.

  Robert Alan May, R Scott Smith, Bruce D Kay
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  ABSTRACT: We investigate the mobility of supercooled liquid toluene, ethylbenzene, and benzene near their respective glass transition temperatures (Tg). The permeation rate of Ar, Kr, and Xe through the supercooled liquid created when initially amorphous overlayers are heated above their glass transition temperature is used to determine the diffusivity. Amorphous benzene crystallizes at temperatures well below its Tg and as a result the inert gas underlayer remains trapped until the onset of benzene desorption. In contrast, for toluene and ethylbenzene the onset of inert gas permeation is observed at temperatues near Tg. The inert gas desorption peak temperature as a function of the heating rate and overlayer thickness is used to quantify the diffusivity of supercooled liquid toluene and ethylbenzene from 115 K to 135 K. In this temperature range, diffusivities are found to vary across five orders of magnitude (~10 14 to 10 9 cm2/s). The diffusivity data are compared to viscosity measurements and reveal a breakdown in the Stokes-Einstein relationship at low temperatures. However the data are well fit by the fractional Stokes-Einstein equation with an exponent of 0.66. Efforts to determine the diffusivity of a mixture of benzene and ethylbenzene are detailed, and the effect of mixing these materials on benzene crystallization is explored using infrared spectroscopy.
  The Journal of Physical Chemistry A 06/2013;
• Article: Ab Initio Chemical Kinetics for H + NCN: Prediction of NCN Heat of Formation and Reaction Product Branching via Doublet and Quartet Surfaces.

  Wen-Shuang Teng, Lyudmila Moskaleva, Hui-Lung Chen, Ming-Chang Lin
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  ABSTRACT: The reaction of NCN with H atoms has been investigated by ab initio MO and RRKM theory calculations. The mechanisms for formation of major products on the doublet and quartet potential energy surfaces have been predicted at the CCSD(T) level of theory with the complete basis set limit. In addition, the heat of formation for NCN predicted at this rigorous level and those from 5 isogyric reactions are in close agreement with the best value based on the isodesmic process, 3CCO + N2 = 3NCN + CO, 109.4 kcal/mol, which lies within the two existing experimental values. The rate constants for the 3 possible reaction channels, H + NCN-->CH + N2 (kP1), HCN + 4N (kQP1) and HNC + 4N (kQP2), have been calculated in the temperature range 298-3000 K. The results show that kP1 is significantly higher than kQP1 and kQP2 and that the total rate constant agrees well with available experimental values in the whole temperature range studied. The kinetics of the reverse CH + N2 reaction has also been revisited at the CCSD(T)/CBS level; the predicted total rate constants at 760 Torr Ar pressure can be represented by kr = 4.01×10-15 T0.90 exp(-17.42 kcal mol-1/RT) cm3 molecule-1 s-1 at T = 800-4000 K. The result agrees closely with the most recent experimental data and the best theoretical result of Harding et al. (J. Phys. Chem. A, 2008, 112, 522) as well as that of Moskaleva and Lin (Proc. Combust. Inst. 2000, 28, 2393) evaluated with a steady-state approximation after a coding error correction made in this study.
  The Journal of Physical Chemistry A 06/2013;
• Article: Weak Ion-Molecule Interactions in the Gas Phase: a High Pressure Mass Spectrometry and Computational Study of Chloride-Alkane Interactions.

  Blake Eric Ziegler, Tanya N Gamble, Chun Li, Terry Brian McMahon
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  ABSTRACT: High pressure mass spectrometric equilibrium experiments and electronic structure calculations have been carried out to investigate the energetics of the interactions of chloride ion with a series of normal and cyclo-alkanes in the gas phase. The structures of the complexes obtained from the electronic structure calculations provide considerable insight into the nature of the interaction between the negatively charged ion and the alkanes, which has the character of a purely ion-induced dipole interaction. The structural information also shows how the charged species affect the confirmation of the normal alkanes.
  The Journal of Physical Chemistry A 06/2013;
• Article: The Effects of Microhydration on the Electronic Properties of Ortho-Aminobenzoic Acid.

  Vanusa Bezerra Pachêco, Puspitapallab Chaudhuri
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  ABSTRACT: High-level density functional electronic structure calculations have been performed to analyze the effect of microsolvation with water on the electronic properties of ortho-aminobenzoic acid (o-Abz). The hydrogen-bonded interaction of o-Abz molecule with one upto three water molecules, o-Abz•••(H2O)n, (n = 1-3) have been considered in two different situations: once the solvent water molecules are placed close to the carboxyl (-COOH) group of o-Abz producing the "o-Abz ⋯(H2O) _n^COOH" complexes and then the water molecules placed close to the amino (-NH2) group producing the "o-Abz ⋯(H2O) _n^NH2" clusters. Variation of the vibrational spectra and energetics upon hydrogen-bond formation are analyzed and compared with available experimental data. The effect of cooperativity is also analyzed. Overall, the hydrogen-bonded "o-Abz ⋯(H2O) _n^COOH" clusters are found to be more stable than the "o-Abz ⋯(H2O) _n^NH2" clusters.
  The Journal of Physical Chemistry A 06/2013;