Quantum Dynamics of Nonadiabatic Renner–Teller Effects in Atom + Diatom Collisions

Abstract

We review the quantum nonadiabatic dynamics of atom + diatom collisions due to the Renner–Teller (RT) effect, i.e., to the Hamiltonian operators that contain the total spinless electronic angular momentum L̂. As is well-known, this rovibronic effect is large near collinear geometries when at least one of the interacting states is doubly degenerate. In general, this occurs in insertion reactions and at short-range, where the potential wells exhibit deep minima and support metastable complexes. Initial-state-resolved reaction probabilities, integral cross sections, and thermal rate constants are calculated via the real wavepacket method, solving the equation of motion with an approximated or with an exact spinless RT Hamiltonian. We present the dynamics of 10 single-channel or multichannel reactions showing how RT effects depend on the product channels and comparing with the Born–Oppenheimer (BO) approximation or coexisting conical-intersection (CI) interactions. RT effects not only can significantly modify the adiabatic dynamics or correct purely CI results, but also they can be very important in opening collision channels which are closed at the BO or CI level, as in electronic-quenching reactions. In the OH­(A2Σ+) + Kr electronic quenching, where both nonadiabatic effects (CI and RT) coexist, they are in competition because CI dominates the reactivity but RT couplings reduce the large CI cross section and open a CI-forbidden evolution toward products, so that CI + RT quantum results are in good agreement with experimental or semiclassical findings. The different roles of these couplings are due to the unlike nuclear geometries where they are large: rather far from or near to linearity for CI or RT, respectively. The OH­(A2Σ+) + Kr electronic quenching was investigated with the exact RT Hamiltonian, validating the approximated one, which was employed for all other collisions.

Electronically Nonadiabatic Effects on the Quantum Dynamics of the Ha + BeHb+ → Be+ + HaHb; Hb + BeHa+ Reactions

“…Previous studies have shown that the RT effects not only can significantly affect dynamics characteristics but also can correct pure CI results when both the interactions coexist. 11,12 In fact, electronically nonadiabatic effects have been shown to play a profound role in many chemical processes, such as photodissociation, 13,14 charge transfer, 15−17 and collisional quenching. 18−21 On the one hand, some products can be generated only by nonadiabatic transitions when the chemical reaction processes involve excited-state reactants.…”

“…Another important example is the Renner–Teller (RT) coupling, − that is, the interacting electronic states have the degenerate components at the collinear configurations. Previous studies have shown that the RT effects not only can significantly affect dynamics characteristics but also can correct pure CI results when both the interactions coexist. , …”

Neglected Importance of Anharmonicity in Quantifying the Renner–Teller Effect

“…This in turn confirms Dressler and Ramsay’s attributing of the absorption spectrum to transitions between two real components of the Π state (Figure c). Other illustrations, where the RT effect plays an important role, include enhancement of magnetism of luminescence properties by suppressing RT vibronic coupling or restriction of RT distortion, bond stretch isomerism, chemistry involving continuum processes, or anomaly dynamic behaviors …”

“…Other illustrations, where the RT effect plays an important role, include enhancement of magnetism of luminescence properties by suppressing RT vibronic coupling or restriction of RT distortion, 10 bond stretch isomerism, 11 chemistry involving continuum processes, 12 or anomaly dynamic behaviors. 13 …”