UV absorption spectrum and photodissociation dynamics of CH2OO following excitation to the B1 A′ state

The spectroscopy and dynamics of the smallest Criegee intermediate CH2OO following UV excitation to the B state is studied theoretically, based on multireference electronic wave functions and a quantum dynamical approach for the nuclear motion. Two interacting electronic states and two nuclear degrees of freedom are considered in the dynamical treatment. The UV absorption spectrum is found to agree very well with available experimental recordings when accounting for broadening effects due to vibrational and rotational congestion and lifetime effects. Upon higher resolution two different energetic regimes can be approximately distinguished, a higher-energy regime where the spectral envelope is broad and structureless, and dissociation is prompt, and a lower-energy regime featuring narrow resonances which are supported by the shallow well occurring at intermediate O-O distances, and decay by tunnelling to the repulsive outer part of the potential energy surface. The importance of nonadiabatic coupling effects is pointed out and future steps for an improved theoretical treatment are outlined. [GRAPHICS] .

Automated summary

The spectroscopy and dynamics of the smallest Criegee intermediate CH2OO following UV excitation to the B state have been theoretically studied. Two distinct energetic regimes, distinguished based on higher resolution UV absorption spectrum, reveal the prompt dissociation in a higher-energy regime and narrow resonances in a lower-energy regime within the system. Additionally, the importance of nonadiabatic coupling effects and future steps for improved theoretical treatment are outlined.