Remarkable impact of intermode couplings on multimode vibronic dynamics: The photoelectron spectrum of CH ₃F

Electronic and nuclear motions on intersecting potential energy surfaces are often intricately mixed and the spectrum can become very complex. Here we choose the strongly coupled Jahn-Teller system C H3 F+ as a prototype example, and establish the importance of intermode coupling terms on multimode vibronic dynamics. The theoretical approach consists of a full second-order diabatic vibronic Hamiltonian, constructed from high-quality electronic structure calculations. Our results compare amazingly well with the experimental data. This highlights the success of the present theoretical approach in explaining the complex structure of vibronic spectra, ubiquitous in molecular systems.