Signatures of light-induced nonadiabaticity in the field-dressed vibronic spectrum of formaldehyde

Nonadiabatic coupling is absent between the electronic ground X and first excited (singlet) A states of formaldehyde. As laser fields can induce conical intersections between these two electronic states, formaldehyde is particularly suitable for investigating light-induced nonadiabaticity in a polyatomic molecule. The present work reports on the spectrum induced by light-the so-called field-dressed spectrum-probed by a weak laser pulse. A full-dimensional ab initio approach in the framework of Floquet-state representation is applied. The low-energy spectrum, which without the dressing field would correspond to an infrared vibrational spectrum in the X-state, and the high-energy spectrum, which without the dressing field would correspond to the X -> A spectrum, are computed and analyzed. The spectra are shown to be highly sensitive to the frequency of the dressing light allowing one to isolate different nonadiabatic phenomena.

Automated summary

This study explores light-induced nonadiabaticity in formaldehyde by inducing conical intersections between the X and A states using laser fields. The field-dressed spectrum is probed by a weak laser pulse and analyzed using a full-dimensional ab initio approach in the Floquet-state representation. The resulting spectra are highly influenced by the frequency of the dressing light, allowing for the isolation of different nonadiabatic phenomena.