Tracing potential energy surfaces of electronic excitations via their transition origins: application to Oxirane

TL;DR

This paper introduces a method using transition origins from QNTO analysis to connect potential energy surfaces across geometries, demonstrated on oxirane, aligning with experimental and high-level theoretical results.

Contribution

It presents a novel approach to trace potential energy surfaces via transition origins, applicable to complex molecules, enhancing understanding of electronic excitations during reactions.

Findings

Transition origins can connect PESs across geometries.

The method corroborates experimental Gomer-Noyes mechanism.

Applicable to larger, complex molecular systems.

Abstract

We show that the transition origins of electronic excitations identified by quantified natural transition orbital (QNTO) analysis can be employed to connect potential energy surfaces (PESs) according to their character across a widerange of molecular geometries. This is achieved by locating the switching of transition origins of adiabatic potential surfaces as the geometry changes. The transition vectors for analysing transition origins are provided by linear response time-dependent density functional theory (TDDFT) calculations under the Tamm-Dancoff approximation. We study the photochemical CO ring opening of oxirane as an example and show that the results corroborate the traditional Gomer-Noyes mechanism derived experimentally. The knowledge of specific states for the reaction also agrees well with that given by previous theoretical work using TDDFT surface-hopping dynamics that was validated by high-quality quantum Monte Carlo calculations. We also show that QNTO can be useful for considerably larger and more complex systems: by projecting the excitations to those of a reference oxirane molecule, the approach is able to identify and analyse specific excitations of a trans-2,3-diphenyloxirane molecule.