Photodissociation of ketene: CH{sub 2}CO {yields} CH{sub 2}(a{sup 1}A{sub 1}) + CO(v=1) rates and dynamics

The rotational energy release in the dissociation of ketene (CH{sub 2}CO) along its singlet potential energy surface is observed and compared with several statistical and dynamical theories. Rotational distributions for the product, CO(X{sup 1}{Sigma}+)(v=1), are measured from the threshold for production of CH{sub 2}(a {sup 1}A{sub 1}) (0,0,0) + CO(X{sup 1}{Sigma}+)(v=1) to 1720 cm{sup -1} above. Near threshold (E{le} 200 cm{sup -1} over threshold), phase space theory (PST) matches the observed distributions. At 357 and 490 cm{sup -1}, PST constrained by the measured state distributions of the methylene fragment, provides a good fit to these CO(v=1) rotational distributions. For E > 490 cm{sup -1}, the constrained PST matches the average rotational energy observed but predicts distributions which are broader than observed. This contrasts to the rotational distributions of the {sup 1}CH{sub 2} fragment which become shifted to lower rotational states than PST as energy increases from 200 cm{sup -1} above threshold. Dynamical models, the impulsive model and Franck-Condon mapping, do not account for the product rotational state distributions. The CO(v=1) rotational distributions for E > 200 cm{sup -1} contain no measurable product from triplet channel fragmentation. Therefore, they can be compared with the previously determined CO(v=0) rotational distributions in order to partition the CO(v=0) yield between singlet and triplet channels and recalculate the singlet yield. This new yield is found to be at the upper limits of the range previously reported. Rate constants and quantum yields have been determined for the photodissociation of ketene to produce CH{sub 2}(a {sup 1}A{sub 1}) (0,0,0) + CO(X {sup 1}{Sigma}+)(v=1). At 57, 110, 200, 357, and 490 cm{sup -1} above this product threshold, vibrational branching ratios for the singlet products were measured and compared to phase space theory (PST), separate statistical ensembles (SSE), and variational RRKM (var. RRKM)