The vibrational predissociation dynamics of ArCl2: Intramolecular vibrational relaxation in a triatomic van der Waals molecule?

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Abstract
Rotational–vibrational distributions are reported for Cl2 product states of the vibrational predissociation of the v=6 through v=12 levels of the ArCl2 molecule in the B electronic state. For v=6 and 7, the Δv=−1 dissociation channel dominates the predissociation dynamics, and the observed rotational distribution appears to be slightly inverted. This inversion does not appear to be due to ‘‘momentum gap’’ constraints but may be due to kinematic symmetry selection rules. Above v=7 the molecule decays via the Δv=−2 channel. Unlike the rotational distributions observed for HeCl2 and NeCl2, those of the ArCl2 Δv=−2 channel are highly structured and have a strong dependence on the initially excited vibrational level. It is argued that the dependence of the observed rotational distribution on the initial vibrational state (for the dissociation of ArCl2) is due to intermediate resonances in a sequential, IVR mechanism, whereas the dissociation of HeCl2 and NeCl2 occurs by a direct mechanism. Although this conclusion cannot be proved at this time, experiments and calculations are suggested that would directly measure the participation of intermediate levels.