Photodissociation dynamics of methyl vinyl ketone oxide: A four-carbon unsaturated Criegee intermediate from isoprene ozonolysis

The electronic spectrum of methyl vinyl ketone oxide (MVK-oxide), a four-carbon Criegee intermediate derived from isoprene ozonolysis, is examined on its second pi* & LARR; pi transition, involving primarily the vinyl group, at UV wavelengths (lambda) below 300 nm. A broad and unstructured spectrum is obtained by a UV-induced ground state depletion method with photoionization detection on the parent mass (m/z 86). Electronic excitation of MVK-oxide results in dissociation to O (D-1) products that are characterized using velocity map imaging. Electronic excitation of MVK-oxide on the first pi* & LARR; pi transition associated primarily with the carbonyl oxide group at lambda > 300 nm results in a prompt dissociation and yields broad total kinetic energy release (TKER) and anisotropic angular distributions for the O (D-1) + methyl vinyl ketone products. By contrast, electronic excitation at lambda & LE; 300 nm results in bimodal TKER and angular distributions, indicating two distinct dissociation pathways to O (D-1) products. One pathway is analogous to that at lambda > 300 nm, while the second pathway results in very low TKER and isotropic angular distributions indicative of internal conversion to the ground electronic state and statistical unimolecular dissociation.

Automated summary

The study examined the electronic spectrum of MVK-oxide on its second pi* & LARR; pi transition below and above 300 nm UV wavelengths, revealing different dissociation pathways and product characteristics upon electronic excitation.