Photodissociation dynamics of methyl formate at 193.3 nm: Branching ratios, kinetic-energy distributions, and angular anisotropies of products

Abstract

We investigated the photodissociation dynamics of methyl formate-d (CH(3)OC(O)D) at 193.3 nm in a molecular-beam apparatus using undulator radiation as an ionization source. We measured kinetic-energy distributions, spatial angular anisotropies, and branching ratios of all photofragments. Fractions of energy release into product translation were calculated from the kinetic-energy distributions. Four primary dissociation pathways to asymptotes CH(3)O(X (2)E)+DCO(X (2)A(')), CH(3)O(X (2)E)+DCO(A (2)A(")), CH(3)OCO(X (2)A('))+D((2)S), and CH(3)OD(X (1)A('))+CO(X (1)Sigma(+)) were identified; their branching ratios were determined to be 0.73, 0.06, 0.13, and 0.08, respectively. The former two dissociation paths were discernible in the time-of-flight spectra of fragment CH(3)O with a signal at m/z=29. Nominal products DCO (A (2)A(")) and CH(3)OCO (X (2)A(')) were unobservable as DCO in state A dissociated to D((2)S)+CO(X (1)Sigma(+)) and internally hot CH(3)OCO (X (2)A(')) decomposed to CH(3)(X (2)A(2) ("))+CO(2)(X (1)A(1g)). Products DCO and CH(3)O have angular anisotropy parameter beta approximately -0.37 but other products have nearly isotropic angular distributions with /beta/<0.1. Nonadiabatic transitions might play an important role in fragmentation of methyl formate irradiated at 193.3 nm.