Photodissociation dynamics of gas-phase BrICl- and IBr2- anions

This work is the first study of mixed trihalide anions in the gas phase. We report the photochemistry and photodissociation dynamics of BrICl- and IBr 2- anions near 400 nm. For BrICl-, two major photodissociation channels yie lding IBr- and ICl- products are observed. The photodissociation of IBr2- y ields primarily IBr- anion products. No BrCl- and Br-2(-) fragments are for med from BrICl- and IBr2-, respectively, and the parent anions are ascribed linear [Br-I-Cl](-) and [Br-I-Br](-) structures, in agreement with ab init io calculations. The IBr- and ICl- products are produced in highly vibratio nally excited states. We observe fragment vibrational coherence in femtosec ond pump-probe measurements by probing nascent IBr- via its photodissociati on to I- + Br. The IBr- vibrational periods observed in the photodissociati on of BrICl- correspond to excitations of similar to 80% of the IBr- dissoc iation energy (D-o). In IBr2- dissociation, the average vibrational excitat ion of IBr- is 84-91% of D-o. The high degrees of vibrational excitation ra ise questions about the effect of the proximity to the dissociation thresho ld on the dynamics of coherent wave packets. We analyze these dynamics anal ytically and by means of wave packet simulations and observe smearing of ex pected wave packet revivals.