Investigation of the dynamics and energy disposal in the photodissociation of small ion clusters using a high-energy ion beam crossed with a laser beam: Photodissociation of (NO)2+. in the 488–660 nm range

Abstract

The results of a study of the dynamics of photodissociation of the (NO)2+. cluster ion to form NO++NO. in the 488–660 nm range are presented. The experiments were performed by crossing a high energy ion beam with a laser beam. Product kinetic energy distributions were derived from the experimental measurements along with information about the angular distribution of the products. Except at the lowest photon energy at which experiments were performed [where the product relative velocity is comparable to the rotational velocity of (NO)2+.], the product angular distributions could be adequately fit by an angular distribution of the form 1+βP2(θ) with a value for β of 1.3. The product kinetic energy distributions are characteristic of dissociation occurring on a repulsive surface. The fraction of the available energy partitioned into relative kinetic energy increases from 22% at 659 nm to 32% at 488 nm. The data on the product angular distributions indicate that photodissociation occurs by a transition to an excited state with a lifetime that is negligible compared with a rotational period, and that the polarization of the transition is predominantly along the NO–NO+ axis in the cluster. The fraction of available energy partitioned into relative kinetic energy can be accounted for by using a simple impulsive model plus vibrational excitation due to changes in equilibrium geometries of the NO. and NO+ moieties.