Abstract
In theoretical studies of chemical reactions involving multiple potential energy surfaces (PESs) such as photochemical reactions, seams of intersection among the PESs often complicate the analysis. In this paper, we review our recipe for exploring multiple PESs by using an automated reaction path search method which has previously been applied to single PESs. Although any such methods for single PESs can be employed in the recipe, the global reaction route mapping (GRRM) method was employed in this study. By combining GRRM with the proposed recipe, all critical regions, that is, transition states, conical intersections, intersection seams, and local minima, associated with multiple PESs, can be explored automatically. As illustrative examples, applications to photochemistry of formaldehyde and acetone are described. In these examples as well as in recent applications to other systems, the present approach led to discovery of many unexpected nonadiabatic pathways, by which some complicated experimental data have been explained very clearly.
Highlights
In order to theoretically unravel the entire photochemical reaction processes of a given system, one has to explore and characterize systematically several excited as well as the ground state potential energy surfaces (PESs)
We review our recipe for exploring multiple PESs by using an automated reaction path search method which has previously been applied to single PESs
transition states (TSs) on an excited state PES EState 1 can be explored in two steps: a search for many TS-like structures as first-order saddles on FAMF by an automated search method, optimization of true TSs on the PES EState 1 using the TS-like structures as initial guesses
Summary
In order to theoretically unravel the entire photochemical reaction processes of a given system, one has to explore and characterize systematically several excited as well as the ground state potential energy surfaces (PESs). A similar problem sometimes arises in the search for TSs on a single PES To avoid this problem, many automated TS (or minimum energy path) search methods have been developed [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]. AFIR can efficiently explore associative reaction paths among given reactants of multicomponent reactions We apply the proposed recipe with the GRRM method to photodissociation mechanisms of small carbonyl compounds such as formaldehyde H2CO and acetone (CH3)2CO [49, 51]
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