Ab initio quantum chemical calculations for the molecular dissociation chan
nel of acetaldehyde are reported. The enthalpy change for the dissociation
of acetaldehyde into methane and carbon monoxide was calculated to be exoer
gic by 1.7 kcal/mol. The transition state for this unimolecular dissociatio
n, confirmed by normal mode analysis, was found to have an activation energ
y of 85.3 kcal/mol. Experimental measurements are reported for the vibratio
nal and rotational state distribution of the CO product. No v=1 CO is found
and the rotational temperature is 1300 +/- 90 K. The reaction coordinate a
t the transition state implies that the CO product is vibrationally cold an
d rotationally hot. This conclusion, which requires quantum dynamics calcul
ations to confirm definitively, does agree with and aids in explaining the
experimental results. (C) 2001 American Institute of Physics.