Insights into the mechanistic photodissociation of methyl formate

In this work, we studied the photodissociation dynamics of methyl formate (CH3OC(O)H) using state-of-the-art multireference configuration interaction with single and double excitation and the complete active space self-consistent field methods. It was found that the direct alpha-C - O bond cleavage in the first excited singlet state (S-1) is the dominant dissociation channel, consistent with the recent experiment [S. H. Lee, J. Chem. Phys. 129, 194304 (2008)]. This cleavage mechanism is different from that for aldehydes/ketones where it occurs in the lowest triplet state (T-1) as a result of the S-1 -> T-1 intersystem crossing. On the basis of comparison to the alpha-bond fission in the asymmetrically substituted aliphatic carbonyl compounds studied previously, we suggest the photolytic reaction of CH3OC(O)H as a special type of Norrish type I reaction.