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

Abstract

The spectroscopy and dynamics of the smallest Criegee intermediate CH${}_2$OO 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.

GRAPHICAL ABSTRACT

Acknowledgements

It is our pleasure to dedicate this paper to Prof. John Stanton on the occasion of his 60th birthday. The authors would like to thank Prof. H.-D. Meyer for stimulating and fruitful discussions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

We are indebted to the Deutsche Forschungsgemeinschaft (DFG) for financial support (KO 945/22-1).