An ab initio quantum dynamics simulation of UV absorption spectrum of methyl vinyl ketone oxide

The spectroscopy of the four-carbon Criegee intermediate, methyl vinyl ketone oxide (MVK-oxide), following UV excitation to the B state (corresponding to the first π* ← π electronic transition), is studied theoretically, which relied on a single reference electronic wave function and a quantum dynamical approach for the nuclear motion. Two interacting electronic states BA'1 and CA'1, together with two nuclear degrees of freedom (O-O stretching and C-O-O bending modes), are considered in the dynamical approach. The computed absorption spectrum is found to agree well with the available experimental recordings. The existence of the weak oscillatory structures in the absorption spectrum is argued likely due to the fact that the excitation energy range of the first π* ← π electronic transition is below the energy barrier of the diabatic B state (∼215 nm) and, thus, below the sufficiently deep well occurring at the intermediate O-O distances. This suggests the recurrences of the wavepacket, which might be considered the origin of the weak oscillatory structures in the absorption spectrum. The computed electronic excitation profile of MVK-oxide is predicted to peak at 373 nm.