More protected vibrational states at the dissociation limit of SCCl ₂

Local vibrational coupling models predict that intramolecular vibrational energy redistribution (IVR) is not completely statistical even at the dissociation limit of polyatomic molecules. Thus states protected from IVR and from rapid dissociation form regular progressions and can be assigned vibrational quantum numbers. We previously observed such regular progressions of states in vibrational spectra of the molecule SCCl₂, but a discrepancy in the density of such states remained between theory and experiment. Here we show that the gap can be closed by observing and assigning additional vibrational transitions above the dissociation limit of SCCl ₂, and by carefully analyzing the theoretically expected density of protected states. The newly observed transitions originate from recently assigned and more highly excited vibrational levels in the B̃ electronic state, connecting to the X̃ ground state by different Franck-Condon factors. Based on our analysis of Franck-Condon activity, we conclude that theory and experiment agree within measurement uncertainty. Consistency between theory and experiment implies that even more protected states should be observed for larger molecules, leading to nonstatistical dissociation reactions.