Photodissociation dynamics of negative ion clusters: (SO2)−2

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Abstract
The photodissociation dynamics of (SO2)−2 to form SO2/SO−2 products is investigated over the wavelength range 656 (1.89 eV) to 458 nm (2.71 eV). Product angular distributions are obtained. An asymmetry parameter analysis indicates the lifetime of the (SO2)−2 photoexcited state is much less than a rotational period. Product kinetic energy distributions are obtained at all wavelengths. Both the overall shape of these distributions and comparison with statistical phase space theory calculations indicate the excited state assessed by the photon is repulsive consistent with the asymmetry parameter analysis. An impulsive model analysis suggests the bond between the two SO2 moeities in (SO2)−2 is probably between one oxygen atom on each moeity and the structure is quasilinear. Structure is also observed in the kinetic energy distributions. It is suggested this is due to selective photoexcitation of vibrational states of either the SO2 or SO−2 moeity in (SO2)−2. Hodges and Vanderhoff have reported a bimodel photodestruction cross section for (SO2)−2, with major peaks near 600 and 400 nm. We argue these peaks are due to photodissociation of (SO2)−2 not photodetachment, with the first excited doublet state (repulsive) leading to the 600 nm peak and the second excited doublet state (bound) leading to the second maxima. The repulsive state must correlate to ground state SO2/SO−2 products and the bound state to electronically excited SO2/SO−2 products. Predictions regarding the dissociation dynamics of the bound state are made.

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