Rotational effects in the unimolecular dissociation of the acetyl radical

The dissociation dynamics of rotating acetyl radical at energies near the threshold (19–23 kcal/mol) has been investigated by classical dynamics. Under microcanonical initial conditions and with zero total angular momentum, the dissociation of CH3CO is intrinsically RRKM. When the rotational degrees of freedom are taken into account the phase space becomes non-ergodic. At 23 kcal/mol and for 6.7 ps, which is the average lifetime at this energy, between 15% and 40% of Ka space is mixed, suggesting that rotation–vibration coupling is modest, in agreement with experimental findings. Finally, excitation of the torsional mode decreases the rate by a factor of two.