A classical-path surface-hopping study of Mu, H and T hot-atom collisions with F2

Abstract

The collision dynamics of processes pertinent to the hot-atom chemistry of the hydrogen isotopes Mu, H and T with are explored using mixed quantumÈclassical techniques. We use classical-path surface-hopping and F 2 pure classical-path multi-surface trajectory methods with a set of 14 coupled potential energy surfaces (PESs) from a diatomics-in-molecules (DIM) model. We compare with results from the standard quasiclassical trajectory (QCT) method applied to the electronic ground state surface of the same DIM model. We compute reaction-and dissociation cross sections for centre-of-mass collision energies ranging from threshold to 20 eV. In order to quantify the notion of electronic non-adiabaticity we introduce various cross sections measuring electronically non-adiabatic processes. We Ðnd that non-adiabatic e †ects give rise to pronounced changes in the dynamics of the system. In particular, collision-induced dissociation of by Mu is an essentially Mu ] F 2 F 2 electronically non-adiabatic process, proceeding efficiently by a mechanism involving transitions to excited repulsive PESs. In contrast, QCT calculations on the electronic ground state surface predict vanishingly small dissociation cross sections. We also discuss some consequences of this behaviour for simulations of Mu ] F 2 Mu hot-atom chemistry.

Critical appraisal of the fewest switches algorithm for surface hopping

“…This kind of quantum/classical partition is computationally very convenient but suffers several drawbacks due to the complete neglect of the quantum features of the nuclear motion. Moreover, there is no generally accepted definition for a mixed quantum/classical system ͑as observed by Caro and Salcedo, 15 this is because no such systems exist in nature͒ and then, a very large number of quantum/classical schemes have been developed, ranging from methods based on independent trajectories [16][17][18][19] to more complicated approaches in which at least some aspects of the quantum nature of the nuclear motion are retained: full multiple spawning, 20 quantum/classical Liouville dynamics, [20][21][22][23][24][25][26] Bohmian trajectories, 27 path integrals, 28 and many others. [29][30][31][32][33][34] However, the TSH method in its most popular implementation, i.e., Tully's "fewest switches" approach 7 ͑TFS͒, is still a good compromise between computational efficiency, conceptual simplicity, and accuracy of results, 17 especially for medium-sized and large molecular systems.…”

A general method to describe intersystem crossing dynamics in trajectory surface hopping

“…The latter effect can be partially mitigated using socalled decoherence corrections; the interested reader is referred to the according literature. [132,[136][137][138][139][140][141][142][143][144][145][146][147][148][149][150][151][152][153] Tunneling effects can also not be described with surface hopping although there exist several approaches to alleviate this deficiency, see, for example, Refs. [154][155][156][157][158].…”

Radical kinetics in sub- and supercritical carbon dioxide: thermodynamic rate tuning

“…The reactions of H isotopes are fundamental as they are the simplest atoms. [15][16][17] Generating hydrogen atoms in CO 2 requires an additional species to be used as a precursor for the atom. This brings up several concerns, namely: (1) Can H atoms be generated consistently over the desired range of thermodynamic conditions in CO 2 ?…”