Simulating Ultrafast Transient Absorption Spectra from First Principles using a Time-Dependent Configuration Interaction Probe

• DOI: 10.48550/arxiv.2404.16568
• Publication Date: 2024-04-25
• Authors: C. A. Mehmood; Myles Silfies; Andrew S. Durden; Thomas K. Allison; Benjamin G. Levine
• Keywords: Transient (computer programming)

Transient absorption spectroscopy (TAS) is among the most common ultrafast photochemical experiments, but its interpretation remains challenging. In this work, we present an efficient and robust method for simulating TAS signals from first principles. Excited-state stimulated emission (SE) are computed using time-dependent complete active space configuration interaction (TD-CASCI) simulations, leveraging robustness of time-domain simulation to minimize electronic structure failure. We demonstrate our approach by signal 1$^\prime$-hydroxy-2$^\prime$-acetonapthone (HAN) ab initio multiple spawning nonadiabatic molecular dynamics simulations. Our results compared gas-phase data recorded both jet-cooled ($T\sim 40$ K) hot ($\sim 403$ molecules via cavity-enhanced transient (CE-TAS). Decomposition spectrum allows us assign a rise in SE excited-state proton transfer ultimate decay relaxation through twisted conical intersection. The total cost computing observable ($\sim$1700 graphics processing unit hours $\sim$4 ns electron dynamics) was markedly less than that {\em initio} calculations used compute underlying dynamics.