Rotational effects in the unimolecular dissociation of the acetyl radical

The dissociation dynamics of rotating acetyl radical at energies near the t hreshold (19-23 kcal/mol) has been investigated by classical dynamics. Unde r microcanonical initial conditions and with zero total angular momentum, t he 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, b etween 15% and 40% of K-a space is mixed, suggesting that rotation-vibratio n coupling is modest, in agreement with experimental findings. Finally, exc itation of the torsional mode decreases the rate by a factor of two. (C) 20 00 Elsevier Science B.V. All rights reserved.