Photodissociation of weakly bound ion-molecule clusters: krypton-sulfur dioxide (Kr.SO2+)

Abstract

A photodissociation study of Kr.SO/sub 2//sup +/ is presented. Kr.SO/sub 2//sup +/ was formed by three-body recombination of SO/sub 2//sup +/ with Kr in a high-pressure ion source. Two ionic products, Kr/sup +/ and SO/sub 2//sup +/, were observed when the ion beam was crossed with a focused laser beam. Wavelengths of 458, 488, 514 and 585 nm were used. Product relative kinetic energy distributions, product angular distributions (asymmetry parameters), and product branching ratios were obtained. A statistical phase space calculation was carried out for the SO/sub 2//sup +//Kr product channel. These results suggest either the SO/sub 2//sup +/ product is both vibrationally and electronically excited or a new electronic state of SO/sub 2//sup +/ at approx.1.5 eV is formed. Product relative kinetic energy distributions and angular distributions suggest the Kr/sup +/ ionic product is produced nonstatistically, probably via direct transition to a repulsive state(s) that correlate to Kr/sup +/(/sup 2/P/sub 3/2/)/SO/sub 2/ products. The Kr/sup +//SO/sub 2/ and SO/sub 2//sup +//Kr products come from two noninterconverting sets of photoexcited states. The lifetime of the state(s) leading to Kr/sup +//SO/sub 2/ products is substantially less than a rotational period of the Kr.SO/sub 2//sup +/ cluster while the lifetime of themore » states leading to SO/sub 2//sup +//Kr products is equal to or somewhat larger than a rotational period. The branching ratio varies form 53% Kr/sup +//SO/sub 2/ at 458 nm to 21% Kr/sup +//SO/sub 2/ at 585 nm and reflects changes in the absorption cross sections to the two sets of noninterconverting excited states from the Kr.SO/sub 2//sup +/ ground state. The data provide an upper bound of 0.30 eV for the bond dissociation energy of Kr-SO/sub 2//sup +/ and indicate the cluster has the structure Kr.OSO/sup +/ not Kr.S(O/sub 2/)/sup +/.« less