Cl+HD reaction dynamics from quasiclassical trajectory calculation on a new ab initio potential energy surface

Development of the Time-Independent Methods for the Cl + H2/F + HD Reaction Using Hyper-Spherical Coordinates Including (Full) Spin-Orbit Characteristics

Recently, a combined study of high-resolution molecular crossed beam experiment and accurate full-dimensional time-dependent theory, including full spin-orbit characteristics on the effect of electronic spin and orbital angular momenta in the F + HD reaction, was reported by some of us, focusing on the partial wave resonance phenomenon (Science 2021, 371, 936-940). It revealed that the time-dependent theory could explain all of the details observed in the high-resolution experiment. Here, we develop two time-independent close-coupling methods using hyperspherical coordinates, including the two-state model, where only a part of the spin-orbit characteristics is considered, and the six-state model, where the full spin-orbit characteristics is considered. With these two newly developed theoretical models and the adiabatic theoretical model, the detailed reaction dynamics of the F + HD (v = 0, j = 0) reaction and the Cl + H2 (v = 0, j = 0) reaction are investigated and compared. Some of the results are compared with the time-dependent quantum wave packet theory and the experimental observations, and good agreements have been obtained, which suggests the validity of the pure-procession approximation in the six-state model using different theoretical methods. This work demonstrates the ability of the reactive scattering theory including full spin-orbit characteristics for describing the reactions of a halogen atom plus hydrogen molecule and its isotopologues.

Significant Isotope Effects from the Nonadiabatic Couplings in the Cl(2P) + HD(v = 0, j = 0) Reaction

The impact of non-Born-Oppenheimer couplings on the isotopic effects in the reaction of the Cl(2P) atom with the HD (v = 0, j = 0) molecule is investigated with our recently developed nonadiabatic time-independent quantum scattering methods, where the full open-shell characteristics are included in the six-state model, and also with the recently developed two-state model solving by time-independent methods, where part of the open-shell characteristic is included. The same reaction is also calculated with the simple adiabatic model using the lowest adiabatic potential energy surface. Compared with the results from different models, it is found that the reactivity of the Cl + HD → HCl + D channel is significantly overestimated in the adiabatic model. In contrast, the reactivity of the other channel agrees well with the nonadiabatic models. This is due to the van der Waals well in the reactant channel being changed a lot by including the nonadiabatic couplings. These quantum dynamics calculations suggest that sometimes the adiabatic model should be used with caution; otherwise, it may result in significant deviations for some reactions.

Quasiclassical trajectory study of the SiH(4)+H-->SiH(3)+H(2) reaction on a global ab initio potential energy surface

The SiH(4)+H-->SiH(3)+H(2) reaction has been investigated by the quasiclassical trajectory (QCT) method on a recent global ab initio potential energy surface [M. Wang et al., J. Chem. Phys. 124, 234311 (2006)]. The integral cross section as a function of collision energy and thermal rate coefficient for the temperature range of 300-1600 K have been obtained. At the collision energy of 9.41 kcalmol, product energy distributions and rovibrational populations are explored in detail, and H(2) rotational state distributions show a clear evidence of two reaction mechanisms. One is the conventional rebound mechanism and the other is the stripping mechanism similar to what has recently been found in the reaction of CD(4)+H [J. P. Camden et al., J. Am. Chem. Soc. 127, 11898 (2005)]. The computed rate coefficients with the zero-point energy correction are in good agreement with the available experimental data.

Details and consequences of the nonadiabatic coupling in the Cl(2P) + H2reaction

In an investigation of nonadiabaticity in the Cl + H2 reaction we examine the various coupling terms responsible. By neglecting various of these terms, we show that the spin-orbit coupling in the Cl atom is primarily responsible for non Born-Oppenheimer effects in this reaction, and that the anisotropies in the contributing electronic potential energy surfaces as well as Coriolis terms, are considerably weaker in their effect. Neglect of all coupling except spin-orbit leads to little change in the calculated reaction probabilities both for the Born-Oppenheimer allowed [Cl(2P3/2) + H2] and Born-Oppenheimer forbidden [Cl(2P1/2) + H2] reactions. This implies that one can safely neglect the coupling between different values of the electronic projection quantum number omega. Consequently, the computational effort involved in an accurate quantum scattering treatment of this (and, hopefully, other similar reactions) can be substantially reduced.

Theoretical study of the validity of the Born-Oppenheimer approximation in the Cl + H2 --> HCl + H reaction

Reactivity of the excited spin-orbit state of Cl with H2 to yield ground-state HCl products is forbidden by the Born-Oppenheimer (BO) approximation. We used new ab initio potential energy surfaces and exact quantum scattering calculations to explore the extent of electronic nonadiabaticity in this reaction. In direct contrast to recent experiments, we predict that the BO-allowed reaction of the ground spin-orbit state will be much more efficient than the BO-forbidden reaction of the excited spin-orbit state. Also, Coriolis coupling opens up an electronically nonadiabatic inelastic channel, which competes substantially with reaction.