Dynamics of rotational energy release for dissociation of singlet ketene and the singlet/triplet branching ratio

The rotational energy release in the dissociation of ketene along its singlet potential energy surface is observed and compared with various statistical and dynamical theories. Rotational distributions for CO(X̃ ¹Σ⁺)(v=1) are measured from the threshold for production of CH₂(ã ¹A₁)(0,0,0) + CO(X̃ ¹Σ⁺)(v=1) to 1720 cm^-1 above. At low energies (≤200 cm^-1), phase space theory (PST) matches the observed distributions. At 357 and 490 cm^-1, PST, constrained by the measured state distributions of the methylene fragment, provides a good fit. For E ≥ 1107 cm^-1, the constrained PST matches the average rotational energy observed but gives distributions which are broader than observed. This contrasts with the ¹CH₂ fragment rotations which become progressively colder than PST as energy increases from 200 cm^-1 above the threshold. The CO(v=1) rotational distributions for E ≥ 357 cm^-1 contain no measurable product from triplet channel fragmentation. They can be compared with the previously determined CO(v=0) rotational distributions in order to partition the yield between singlet and triplet channels and recalculate the singlet yield. This yield is found to be at the upper limit of the range previously reported.