High resolution photofragment translational spectroscopy using Rydberg tagging methods

Photofragment translational spectroscopy (PTS) is a general and versatile technique for exploring the dynamics of gas-phase molecular photodissociation processes, through measurement of the speeds and directions of the resulting atomic and molecular products. This article describes recent enhancements in the achievable kinetic energy resolution and then focuses on applications employing one particular high-resolution variant of the technique, wherein H(D) atom photofragments are monitored by Rydberg tagging methods. Systems described range from small hydrides such as H2O, NH3, and C2H2 to larger heteroaromatic molecules such as pyrrole and phenol. In the former cases, the achievable resolution allows observation of individual rovibrational quantum states of the radical partner, providing detailed insights into the forces acting during the dissociation process. This allows intimate contact with complementary ab initio and wave packet modeling studies, and accurate determination of bond strengths and related thermodynamic quantities. The density of possible product states increases rapidly for larger radical cofragments. PTS studies of several heteroaromatics point to the generality of prompt dissociation from 1πσ* excited states, which manifests itself in remarkably mode specific fragmentation dynamics. The article concludes with a summary of complementary photofragmentation studies of hydride radicals and an anticipation of future activities in this field.