Unraveling vibronic interactions in molecules functionalized with optical cycling centers

TL;DR

This paper characterizes vibronic interactions between excited states in SrOPh molecules, revealing how state mixing affects optical properties and implications for laser cooling of complex molecules.

Contribution

It provides a detailed theoretical and experimental analysis of vibronic state mixing in SrOPh, including modeling with the KDC Hamiltonian and quantifying coupling strength.

Findings

Vibronic interactions cause state mixing in SrOPh.

Deuteration enhances state mixing due to smaller energy gaps.

Effective coupling strength is approximately 0.5 cm-1.

Abstract

We report detailed characterization of the vibronic interactions between the first two electronically excited states, A and B, in SrOPh (Ph = phenyl, -C6H5) and its deuterated counterpart, SrOPh-d5 (-C6D5). The vibronic interactions, which arise due to non-adiabatic coupling between the two electronic states, mix the B,v0 state with the energetically close vibronic level A,v21v33, resulting in extra transition probability into the latter state. This state mixing is more prominent in the deuterated molecule because of the smaller energy gap between the interacting states. We model the mixing of the A and B states using the Koppel-Domcke-Cederbaum (KDC) Hamiltonian parametrized in the diabatic framework of Ichino, Gauss, and Stanton on the basis of equation-of-motion coupled-cluster calculations. The simulation attributes the observed mixing to a second-order effect mediated by linear quasi-diabatic couplings between the A-C and B-C states. Based on the measured spectra, we deduce an effective coupling strength of 0.5 cm-1. Non-adiabatic couplings between different electronic states is an important factor that should be considered in the design of laser-cooling protocols for complex molecules.