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The rate constants for H2 -HF energy transfer processes, especially for those in vibrationally excited states, are very demanding in astrophysics and chemical laser engineering, especially for those in vibrationally excited states. Based on our recent potential energy surface, we used the coupled-states approximation including the nearest neighboring Coriolis couplings with energy-based local basis set to perform dynamics calculation for the H2 -HF energy transfer system. Rate constants for vibrational transitions (1; 3) → (0; 4), (1; 3) → (2; 2), and (0; 3) → (1; 2) were obtained. For state-to-state rate constants, transitions that have no internal angular momentum gap dominate at high temperatures. The vibrational-resolved rate constant for (1; 3) → (0; 4) initially decreases and then increases with the temperature, while those for (1; 3) → (2; 2), and (0; 3) → (1; 2) transitions monotonically increase. The calculated rate constants are in good agreement with the available experimental results. These dynamical data can be further applied to the numerical simulation of hydrogen fluoride chemical laser. © 2018 Wiley Periodicals, Inc.

Much progress has been achieved in the developments of accurate and efficient algorithms for quantum dynamics calculations in the past two decades. Based on the reliable potential energy surfaces (PESs) constructed with state-of-the-art ab initio calculations, quantum reactive scattering calculations for the atom-diatom collisions can be performed accurately at the state-to-state level. In this review, we described the general strategies of constructing a PES and the Chebyshev real wave packet method briefly, and summarized our recent studies on the PESs and state-to-state reaction dynamics for the reactions of the atom N with radicals OH, CH, and C2. Such barrierless complex-forming reactions are very important for understanding low-temperature reaction dynamics and still difficult to treat accurately. © 2014 Wiley Periodicals, Inc.

Pure In2O3 is considered as an efficient methanol steam reforming catalyst. Despite of several studies in the past decades, the mechanism of MSR on In2O3 is still not fully understood. In this work, a periodic density functional theory study of the initial dissociation of methanol and water over the In2O3 (110) surface is presented. The activation energy barriers and thermochemistry for several elementary steps are reported. It is found that the energy barriers for OH bond cleavage of both CH3OH and H2O to produce CH3O and OH species at a surface In-O pair site are very low, indicating that In2O3 (110) can facilely catalyze these two important processes at low temperatures. In addition, the subsequent dehydrogenation of CH3O to CH2O is also found to proceed with a low barrier.

New ab initio potential energy surfaces for the ground (X̃1A') and excited (Ã1A″) electronic states of HSiCl were obtained by using the single and double excitation coupled-cluster theory with a noniterative perturbation treatment of triple excitations and the multi-reference configuration interaction with Davidson correction, respectively, employing an augmented correlation-consistent polarized valence quadruple zeta basis set. For the excited state Ã1A″, an extended active space (18 electrons in 12 orbitals) was used. The calculated vibrational energy levels of HSiCl and DSiCl of the ground and excited electronic states are in better agreement with the available experimental values than the previous theoretical results. In addition, with the calculated transition dipole moment, the absorption and emission spectra of HSiCl and DSiCl were calculated using an efficient single Lanczos propagation method and are in reasonable agreement with the available observed spectra.

We present the minimum-energy structures and energetics of clusters of the linear N2O molecule with small numbers of para-hydrogen molecules with pairwise additive potentials. Interaction energies of (p-H2)–N2O and (p-H2)–(p-H2) complexes were calculated by averaging the corresponding full-dimensional potentials over the H2 angular coordinates. The averaged (p-H2)–N2O potential has three minima corresponding to the T-shaped and the linear (p-H2)–ONN and (p-H2)–NNO structures. Optimization of the minimum-energy structures was performed using a Genetic Algorithm. It was found that p-H2 molecules fill three solvation rings around the N2O axis, each of them containing up to five p-H2 molecules, followed by accumulation of two p-H2 molecules at the oxygen and nitrogen ends. The first solvation shell is completed at N = 17. The calculated chemical potential oscillates with cluster size up to the completed first solvation shell. These results are consistent with the available experimental measurements. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009

An ab initio potential energy surface for the Ar-OCS dimer was calculated using the coupled-cluster singles and doubles with noniterative inclusion of connected triples [CCSD(T)] with a large basis set containing bond functions. The interaction energies were obtained by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The CCSD(T) potential was found to have two minima corresponding to the T-shaped and the collinear ArSCO structures. The two-dimensional discrete variable representation method was employed to calculate the rovibrational energy levels for five isotopomers ArOCS, ArOC34S, ArO13CS, Ar18OCS, and Ar17OCS. The calculated pure rotational transition frequencies for the vibrational ground state of the five isotopomers are in good agreement with the observed values. The corresponding microwave spectra show that the b-type transitions (Δ Ka = ±1) are significantly stronger than the a-type transitions (Δ Ka = 0). Minimum-energy structures of the Ar2OCS trimer were been determined with MP2 optimization, whereas the minimum-energy structures of the ArnOCS clusters with n = 3–14 were obtained with the pairwise additive potentials. It was found that there are two minima corresponding to one distorted tetrahedral structure and one planar structure for the ternary complex. The 14 nearest neighbor Ar atoms form the first solvation shell around the OCS molecule. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1045–1053, 2006

Hydrogen bonding involving azine and its derivatives such as nucleic bases is very important for understanding the structure and function of biological systems. In this work, we have investigated the hydrogen bonding structures of the hydrated cluster and dilute aqueous solution of s-tetrazine using computer simulation techniques, and evaluated the absorption and fluorescence shifts of the lowest 1(n, pi*) excitation of s-tetrazine solution using our solvent shift method. For the s-tetrazine-water cluster, a linear orthodox hydrogen bond arrangement is predicted in both ground and excited states with small structural and energetic differences, and a bifurcated hydrogen bond isomerization is anticipated. Further, ab initio calculations have verified these conformations. For the s-tetrazine-water solution, a mixture of two hydrogen bonding arrangements is found to be in both ground and excited states, resulting in small magnitudes of absorption and fluorescence solvent shifts. This finalizes our series investigation of hydrogen bonding and solvent shifts of dilute azines in water.

The tautomerization equilibria of 3-hydroxy-2-mercaptopyridine (HMP) and 2,3-dihydroxypyridine (DHP) in vacuo and in ethanol solution have been studied using the density functional theory (DFT) at B3LYP/6-31G(d) level. The results indicate that the thione form of HMP and the keto form of DHP are the most stable tautomers in the equilibrium, and the energy barrier for the thiol–thione and enol–keto proton transfer decreases significantly when the tautomerism is mediated by a specific ethanol molecule in solution. The time-dependent density functional theory—polarizable continuum model (TDDFT-PCM) calculations on all tautomers of HMP and DHP in vacuo and in ethanol have assigned the lowest π → π* excitations of thione and keto tautomers to the observed absorption bands of HMP and DHP in solutions. The solvation is predicted to have relatively small effect on these π → π* excitations in ethanol. © 2004 Wiley Periodicals, Inc. J Comput Chem 25: 1833–1839, 2004

Density functional theory calculations have been carried out for hydrogen adsorption on an Rh(111) surface for three surface cells (2 × 2), (√3 × √3) and (1 × 1). Geometrical structures were optimized to determine the chemisorption energies. The diffusion barriers and vibrational frequencies for hydrogen adsorbed on Rh(111) have also been evaluated. The 3-fold hollow site was found to be the most stable site. The effect of surface relaxation was also investigated and found to be small. The calculated vibrational frequencies of 80∼105 and 133∼140 meV at the 3-fold hollow site were attributed to the asymmetric and symmetric stretching modes of H atom, respectively, and in very good agreement with the observed vibrational frequencies of 79∼90 and ∼135 meV.

The reaction pathways for CH3COCH2OH (hydroxyacetone) photodissociation on the low-lying electronic states have been studied with use of the CASSCF energy gradient techniques. The S0/S1 and S1/T1 intersection points were determined by the state-average CASSCF method. Two main reaction pathways, which are possible to the photodissociation, have been studied. It has been found that the mechanism is stepwise, and belongs to Norrish type-I reaction. The n → π* excitation leads to the first excited singlet state, followed by the intersystem crossing from S1 to T1. On the T1 potential energy surface, the system can dissociate adiabatically to CH3(x) +COCH2OH( x) and CH3CO(x)+CH2OH(x). The COCH2OH(x) and CH3CO(x) radicals can further dissociate into CO, OH, and other fragments. Our calculated results are in good agreement with recent experimental results. © 2003 Wiley Periodicals, Inc. J Comput Chem 8: 931–938, 2003

Accurate knowledge of the potential energy surface (PES) and the spectroscopic properties of carbon dioxide plays an important role in understanding the greenhouse effect. The potential energy surface for the electronic ground state of CO{sub 2} is refined by means of a two-step variational procedure using the exact rovibrational Hamiltonian in the bond length-bond angle coordinates. In the refinement, the observed rovibrational energy levels for J = 0-4 below 16,000 cm {sup -1}, obtained from the effective spectroscopic constants of CO{sub 2} given by Rothman et al. (J Quant Spectrosc Radiat Transfer 1992, 48, 537) in HITRAN data base, are used as the input data points. The accurate ab initio force constants of Martin et al. (Chem Phys Lett 1993, 205, 535) are taken as the initial guess for the potential. The root-mean-square error of this fit to the 431 observed rovibrational energy levels is 0.05 cm{sup {minus}1}. With the optimized potential energy surface, the authors also calculate the rovibrational energy levels of {sup 13}C{sup 16}O{sub 2} and {sup 12}C{sup 18}O{sub 2}. The results are in good agreement with experimental data.

Density functional theory with the combined Becke's three-parameter exchange functional in combination with the Lee, Yang, and Parr correlation functional (B3LYP) exchange–correlation energy functions using the 6-31G* basis set was applied to study the structures and vibrational infrared (IR) spectra of 9-methyladenine and the related compounds purine and adenine. The calculated force fields were scaled with the scale factors determined from purine. The predicted vibrational frequencies and isotopic shifts of IR bands of adenine and 9-methyladenine were compared with the available observed matrix-isolated IR spectra with a mean deviation of about 6.4 cm−1. The results made it possible to give reliable assignments of the IR spectra of these molecules. This study shows that the scaled density functional force field approach enables, through the transferability of scale factors, good interpretation of vibrational spectra of large molecules. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 76: 686–699, 2000

A new catalytic method for direct α-selenenylation reactions of aldehydes and ketones has been developed. The results of exploratory studies have demonstrated that l-prolinamide is an effective catalyst for α-selenenylation reactions of aldehydes, whereas pyrrolidine trifluoromethanesulfonamide efficiently promotes reactions of ketones. Under optimized reaction conditions, using N-(phenylseleno)phthalimide as the selenenylation reagent in CH2Cl2 in the presence of l-prolinamide (2 mol %) or pyrrolidine trifluoromethanesulfonamide (10 mol %), a variety of aldehydes and ketones undergo this process to generate α-selenenylation products in high yields. Mechanistic insight into the l-proline and l-prolinamide catalyzed α-selenenylation reactions of aldehydes with N-(phenylseleno)phthalimide has come from theoretical studies employing ab initio methods and density functional theory. The results reveal that (1) the rate-limiting step of the process involves attack of the enamine intermediate at selenium in N-(p...