On the unimolecular dissociation of large molecules

Large molecules excited to well above their dissociation threshold can still have a low mean energy per vibrational mode. The RRK statistical theory predicts rather long decay times for such activated molecules. Yet the dissociation of such molecules can be detected in a mass spectrometer, which requires lifetimes shorter than ≈ 10^-6 s. Qualitative considerations of nonlinear dynamics suggest that the naive RRK theory may well not apply under such circumstances and that the Slater model (interpreted a là KAM), offers a better starting point. Limiting cases when the unimolecular decay rate can be far higher than that calculated by RRK theory for the full complement of degrees of freedom, are discussed.