A comparison of an experimental unimolecular lifetime distribution with Rice–Ramsperger–Kassel–Marcus theory.

The ion–molecule association system (CH+3/CH3CN) has been reexamined by the ion cyclotron double resonance technique. An experimental distribution of lifetimes has been measured for the collision complex (CH3CNCH+3)* formed in the association reaction between CH+3 and CH3CN. The experimental mean lifetime of the association complex formed within the ICR cell was 140 μs. A theoretical examination of the distribution of complex lifetimes using an RRKM model was also undertaken. The matrix of lifetimes for the various values of the total energy of the system (E) and the total angular momentum of the system (J) was obtained. This information was used to visualize the canonical ensemble of collision complexes in the ICR experiment in terms of their lifetimes. Once the distribution of lifetimes predicted by the model was modified to conform to experimental constraints, it was found to give a good approximation of the lifetime distribution determined experimentally. As a result of the new measurements of the complex lifetimes, we report absolute values of the collisional stabilization efficiencies. We also report rate coefficients for unimolecular dissociation and radiative relaxation. [ABSTRACT FROM AUTHOR]