Fully converged integral cross sections of collision induced dissociation, four-center, and single exchange reactions, and accuracy of the centrifugal sudden approximation in H2 + D2 reaction

Abstract

The initial state selected time-dependent wave packet method was employed to calculate the integral cross sections for the H(2) + D(2) reaction with and without the centrifugal sudden (CS) approximation by including all important K (the projection of the total angular momentum on the body-fixed axis) blocks. With a full-dimensional model, the first fully converged coupled-channel (CC) cross sections for different competitive processes from the ground rotational state were obtained: collision induced dissociation (CID), four-center (4C) reaction and single exchange (SE) reaction. The effect of the total angular momentum J on the reaction dynamics of H(2) + D(2) and the accuracy of the CS approximation have also been studied. It was found that the CID and SE processes occur in a wide range of J values while the 4C process can only take place in a narrow window of J values. For this reason, the CC cross section for the 4C channel is merely comparable to the SE channel. A comparison of the integral cross sections from CC and CS calculations showed that the CS approximation works well for the CID process but not for the 4C and SE processes, and the discrepancy between the CC and CS cross sections grows larger as the translational energy and/or the vibrational energy increase(s).

Recent Advances in Development and Applications of the Mixed Quantum/Classical Theory for Inelastic Scattering

“…It cannot really be used directly to compute the cross section at scattering angles smaller than the rainbow angle (see, for example, ref 66), but we found it possible to recover the value of from the dependence. Namely, in the semiclassical treatments of scattering it is assumed that deflection is determined by the total phase shift: (18) If the and dependencies are both known, this expression can be converted into differential equation for with boundary condition , which corresponds to no scattering at large impact parameters. Solving such equation numerically allows reconstructing the dependence:…”

“…13,14 Third, the range of scattering energies we have to cover is often broad, with different mechanisms dominating in different collision regimes (e.g., scattering resonances at low energies 2,12,15 in contrast to vibrational excitation at high energies). [16][17][18] Finally, very detailed information about the process may be needed, such as differential over scattering angle cross section for state-to-state transition. 19,20 If several of these complications have to be tackled simultaneously, the inelastic scattering process does not look simple anymore.…”

STATE-SPECIFIC DISSOCIATION RATES FOR H2(v, j) + H2(v′, j′)

“…To study dissociation, even from states of low internal energies, total energies in excess of 10 eV can be required. Unlike the study of Song et al (2012), in this study both molecules are in low (v, j) states. These states are given in Table 1.…”

“…The work of Song et al (2011aSong et al ( , 2011bSong et al ( , 2012) examined a number of quantum methods including close-coupled and coupled states, and time-dependent wavepacket methods for H 2 +H 2 and isotopic analogs using the potentials of Boothroyd et al (2002a) and Aguado et al (1994). They considered collision-induced dissociation, dissociation with exchange, and four-centered exchange reactions of systems where one of the two diatomics was highly excited and the other in a low v state.…”

The validities of centrifugal sudden approximations in chemical reaction dynamics

“…There has a growing interest in accurately computing the nonadiabatic dynamical quantities of benchmark chemical reactions on several potential energy surfaces (PESs) and in computing the corresponding quantities of tetraatomic and polyatomic chemical reactions. This research interest is motivated by the successful development of the nonadiabatic dynamical methods, in particular of quantum mechanical methods, , and by the great advances in quantum mechanical methods for tetraatomic and polyatomic reactions . However, the inclusion of multiple electronic states in the nonadiabatic treatment and the increase in atom numbers in a reactive system caused extremely difficulty to the quantum scattering calculations due to the rapid increase of basis functions, and a careful examination of CS approximations is essentially helpful in finding a balance between abating such computational difficulty and computational accuracy.…”