Yuzuru Kurosaki

Three-dimensional quantum reactive scattering calculations for the nonadiabatic (D+H2)+ reaction system

Three-dimensional quantum reactive scattering calculations have been carried out for the (D+H2)+ nonadiabatic ion–molecule collision. The calculations have been done using the time-independent close-coupling formalism with hyperspherical coordinates. The (3×3) diatomics-in-molecule potential energy surfaces have been employed. The result of the accurate quantum scattering calculations have been compared to the results of the quasiclassical trajectory surface hopping method. Two versions of the method have been used; one uses Tully’s fewest switches algorithm and the other is the trajectory surface hopping method of Tully and Preston, in which electronically nonadiabatic hopping is only allowed at the predefined crossing seams. We have found that the agreement between the quantum result and the result of Tully’s method is generally good, but the Tully and Preston method significantly underestimates the nonadiabatic transition probability.

van der Waals resonances in cumulative reaction probabilities for the F+H2,D2, and HD reactions

We present accurate quantum cumulative reaction probabilities for the F+H2, D2, and HD reactions with a special emphasis on resonances associated with quasibound states localized in the reactant van der Waals region of the potential energy surface. The accurate ab initio potential surface of Stark and Werner and the less accurate 5SEC-W surface developed by Truhlar and co-workers have been employed. The van der Waals resonance states which occur in the tunneling region can dissociate into the product channel, while the van der Waals resonance states at the classical region dissociate into the reactant channel. This indicates that prereaction effectively occurs in the tunneling region. It has been found that the van der Waals resonance states can be accurately assigned with the eigenvalues calculated with one-dimensional adiabatic potential energy curves.We present accurate quantum cumulative reaction probabilities for the F+H2, D2, and HD reactions with a special emphasis on resonances associated with quasibound states localized in the reactant van der Waals region of the potential energy surface. The accurate ab initio potential surface of Stark and Werner and the less accurate 5SEC-W surface developed by Truhlar and co-workers have been employed. The van der Waals resonance states which occur in the tunneling region can dissociate into the product channel, while the van der Waals resonance states at the classical region dissociate into the reactant channel. This indicates that prereaction effectively occurs in the tunneling region. It has been found that the van der Waals resonance states can be accurately assigned with the eigenvalues calculated with one-dimensional adiabatic potential energy curves.

Quantum scattering calculations for the electronically nonadiabatic Br(2P1/2)+H2→HBr+H reaction

Three-dimensional quantum scattering calculations have been carried out for the electronically nonadiabatic Br(2P1/2)+H2→HBr+H reaction. The calculations have been done using two methods: the time-independent hyperspherical close-coupling formalism for the total angular momentum quantum number J=0 and the generalized R-matrix propagation method with negative-imaginary potentials which absorb the reactive flux for J⩾0, but employing the coupled-states approximation for J>0. The (2×2) diabatic model, which was originally developed by Truhlar and co-workers, has been employed in the present calculations. The results calculated with the two methods agree very well with those obtained by Truhlar and co-workers, indicating that our results are numerically converged. Detailed analyses of the calculated probabilities show that the electronically nonadiabatic transitions from Br(2P1/2)+H2(ν) to Br(2P3/2)+H2(ν+1) effectively occur in the entrance region of the potential surface but that the contribution of the elec...

Photodissociation of acetaldehyde, CH3CHO→CH3+HCO: direct ab initio molecular dynamics study

Abstract A total of 400 trajectories for the photodissociation, CH3CHO→CH3+HCO, on the T1 potential surface have been calculated using the direct ab initio molecular dynamics method at the UB3LYP/cc-pVDZ level of theory. It was predicted that the product CH3 is neither vibrationally nor rotationally excited and HCO is vibrationally not excited but rotationally excited. The averaged HCO rotational energy was calculated to be 1.1 kcal mol−1, which is 15.1% of the available energy, 7.3 kcal mol−1. The present result agrees with experiment within just a few percent of the observed data.

Tunneling in the F+H2 reaction and its isotopic variants: the effect of the Van der Waals potential

Abstract Cumulative reaction probabilities have been calculated for the F+H2, D2 and HD reactions using the three-dimensional quantum scattering method with an emphasis on the threshold behavior of the reaction probabilities. The accurate ab initio potential energy surface of Stark–Werner has been employed. We found small probability peaks just above the reaction threshold for the F+H2 and D2 reactions. These peaks are attributed to the quasi-bound resonance states localized in the reactant Van der Waals well. The results for F+HD also show that the Van der Waals potential plays an important role in reaction dynamics.

Global ab initio potential energy surfaces for the lowest three doublet states (1 2A′, 2 2A′, and 1 2A″) of the BrH2 system

Global adiabatic potential energy surfaces (PESs) of the lowest three doublet states (1 A2A′, 2 2A′, and 1 2A″) for the BrH2 system have been calculated using the multireference configuration interaction (MRCI) method including the Davidson’s correction (Q) with the aug-cc-pVTZ basis set. Spin–orbit effects were considered on the basis of the Breit–Pauli Hamiltonian using the MRCI wave functions. The calculated adiabatic energies were fitted to the analytical functional form of many-body expansion. The barrier heights of the H+HBr→H2+Br abstraction and H+H′Br→H′+HBr exchange reactions on the ground-state PES were calculated to be 1.28 and 11.71 kcal mol−1, respectively, both of which are slightly smaller than the values obtained in the previous work [G. C. Lynch, D. G. Truhlar, F. B. Brown, and J.-G. Zhao, J. Phys. Chem. 99, 207 (1995)]. The fits for the 1 2A′, 2 2A′, and 1 2A″ PESs were successful within an accuracy of 0.1 kcal mol−1 in the important regions of PESs such as the transition states and van ...

Ab initio molecular orbital calculations of potential energy surfaces for the N(, , )+H2 reactions

Abstract Potential energy surfaces for the N( 4 S , 2 D , 2 P )+H 2 reactions have been calculated using the ab initio multireference configuration interaction method. Two-dimensional surfaces were constructed for collinear and perpendicular approaches of N+H 2 in order to understand the mechanisms of these reactions. The calculations predict that not only the lowest doublet surface but also the second lowest doublet surface contribute to the reaction dynamics of N( 2 D )+H 2 and that these two surfaces intersect with the lowest quartet surface of N( 4 S )+H 2 in the intermediate regions. The mechanism of the quenching process for N( 2 P )+H 2 is also discussed.

Theoretical study of kinetic isotope effects on rate constants for the H2+C2H→H+C2H2 reaction and its isotopic variants

Thermal rate constants have been calculated for the H2+C2H→H+C2H2 reaction (1) and its isotopic variants: HD+C2H→H+C2HD (2); DH+C2H→D+C2H2 (3); D2+C2H→D+C2HD (4); H2+C2D→H+C2HD (5) using variational transition state theory with the multidimensional semiclassical tunneling correction. The geometries were optimized at the MP2(full)/cc-pVTZ level and the potential energy curves for these reactions were calculated at the PMP4(SDTQ,full)/cc-pVTZ and QCISD(T,full)/cc-pVTZ levels. It was thus revealed that these reactions have “early” potential barriers. The calculated rate constants for reactions (1) and (5) were found to be comparable and the largest among these reactions. The calculated rate constants for reactions (1) and (4) showed good agreement with experiment at relatively low temperatures. The reaction-path-curvature effects and secondary kinetic isotope effects [the effects of change in zero-point energies (ZPEs) along the reaction path relative to the reactant ZPEs] were predicted not to be so large i...

An ab initio molecular orbital study of even-membered hydrogen cluster cations: H6+, H8+, H10+, H12+, and H14+

Geometries and energetics for even-membered Hn+ (n=6–14) clusters that have the H2+ core in the geometrical structures have been theoretically studied using ab initio molecular orbital methods. It was found that the H2+-core H6+ cluster has D2d symmetry and that the geometrical structures of H2+-core clusters of larger size are composed of unperturbed H2+-core H6+ and outer H2s weakly bound to it. It was predicted for both the H6+ and H8+ clusters that the H2+-core clusters are more stable in energy than the corresponding H3+-core ones. However, the energy difference between H2+- and H3+-core H8+s was calculated to be significantly smaller than that between H2+- and H3+core H6+s. The binding energies of outer H2 in H2+-core clusters were predicted to be 0.7, 0.4, 0.1, and <0.1 kcal mol−1 for H8+, H10+, H12+, and H14+, respectively, at the PMP4(SDTQ)/cc-pVTZ//MP2/cc-pVTZ+ZPE level, suggesting that H8+ and H10+ are stable enough to be detected, but H12+ and H14+ are less stable. This result is consistent wi...

A direct isomerization path for the H6+ cluster.: An ab initio molecular orbital study

Abstract We carried out ab initio molecular orbital calculations for the H 6 + cluster and found two isomers of H 6 + and the transition state (TS) for the direct isomerization. Analysis of the intrinsic reaction coordinate confirmed that the TS is located at the saddle point of the isomerization path. The existence of the direct isomerization path for H 6 + may be one of the reasons for the observation of Kirchner and Bowers that the yield of H 6 + is by far the largest among the even-membered H n + clusters produced.