The rotational distributions of CO products from the dissociation
of ketene at photolysis energies 10 cm{sup {minus}1} below, 56,
110, 200, 325, 425, 1,107, 1,435, 1,720, and 2,500 cm{sup {minus}1}
above the singlet threshold, are measured in a supersonic free jet
of ketene. The CO(v{double_prime} = 0) rotational distributions at
56, 110, 200, 325, and 425 cm{sup {minus}1} are bimodal. The peaks
at low Js, which are due to CO from the singlet channel, show that
the product rotational distribution of CO product from ketene
dissociation on the singlet surface is well described by phase
space theory (PST). For CO(v{double_prime} = 0) rotational
distributions at higher excess energies, the singlet and triplet
contributions are not clearly resolved, and the singlet/triplet
branching ratios are estimated by assuming that PST accurately
predicts the CO rotational distribution from the singlet channel
and that the distribution from the triplet channel changes little
from that at 10 cm{sup {minus}1} below the singlet threshold. At
2,500 cm{sup {minus}1} excess energy, the CO(v{double_prime} = 1)
rotational distribution is obtained, and the ratio of
CO(v{double_prime} = 1) to CO(v{double_prime} = 0) products for the
singlet channel is close to the variational RRKM calculation,
0.038, and the separate statistical ensembles (SSE) prediction,
0.041, but much greater than the PST prediction, 0.016. Rate
constants for the dissociation of ketene (CH{sub 2}CO) and
deuterated ketene (CD{sub 2}CO) have been measured at the threshold
for the production of the CH(D){sub 2} and CO. Sharp peaks observed
in photofragment excitation (PHOFEX) spectra probing CO (v = 0, J =
2) product are identified with the C-C-O bending mode of the
transition state. RRKM calculations are carried out for two
limiting cases for the dynamics of K-mixing in highly vibrationally
excited reactant states.
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