Exploring Multiple Potential Energy Surfaces: Photochemistry of Small Carbonyl Compounds

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.

Automated Exploration of Photolytic Channels of HCOOH: Conformational Memory via Excited-State Roaming

“…These methods can be applied to multiple PESs in combination with the seam model function and avoiding model function approaches. 24,25 By these methods, critical points, that is, minima (MINs) and transition states (TSs) for the ground S 0 , excited singlet S 1 , and lowest triplet (T 1 ) PESs as well as S 0 / S 1 MECIs and S 0 /T 1 and S 1 /T 1 minima on seam of crossing (MSXs), were systematically explored. In the initial search by the GRRM and AFIR methods, SA2-CAS(8e,6o)-SCF/6-31G and CAS(8e,6o)-SCF/6-31G levels were employed for the singlet states and the triplet state, respectively, where SA2 stands for state-average of two states S 0 and S 1 .…”

“…This is very similar to the slow decay mechanism for low-energy photolysis of HCHO, as shown recently. 24,25,36,37 After the decay to the S 0 PES, the molecular dissociation channels to give CO 2 +H 2 (DC1) and CO + H 2 O (DC2) should be dominant because of low corresponding barriers. The quantum yield of HCO + OH channel (DC4) is virtually zero below 252 nm (475 kJ/mol) and gains in intensity with the increasing excitation energy.…”

Multireference Electron Correlation Methods: Journeys along Potential Energy Surfaces

“…Naturally, it benefits greatly from an automated search procedure. Recently, such automated search algorithms were implemented for finding minimal energy points in the seam, − which may be regarded as extensions of automated transition state structure search algorithms − or metadynamics. , This is one of the areas of active development.…”

Discovery of conical intersection mediated photochemistry with growing string methods

“…For example, this was attempted by Maeda and Morokuma with the anharmonic downward distortion following (ADDF) and the artificial-force-induced reaction (AFIR) methods, which have been used to locate MECI. 19–25 Uncovering complete photochemical reaction mechanisms—including MECI, the seam, excited-state TS, and photoproducts—is still a challenging task, however, leaving room for new methodologies.…”