Structure and Dynamics in Highly Excited Molecular States

Bryn Mawr College, Bryn Mawr PA

Investigators

Abstract

The structure and decay dynamics of highly excited states in molecules is a research area that has provided a rich and diverse sampling of interesting and important physics. Investigations of processes such as photoionization, photodissociation, and photo-association have required more detailed and accurate knowledge of the unique way molecular systems behave. In particular, understanding the role of electronic and nuclear spin in molecular systems has emerged as important in several areas, for example, high resolution photoionization studies, chemical reaction dynamics and loss mechanisms in cold molecule production in atomic traps. This has led to new theoretical efforts to incorporate electronic and nuclear spin dynamics into the highly successful theoretical approach of multichannel defect theory (MQDT). Fundamental questions are being raised, including: 1) How does spin angular momentum coupling vary with energy in molecular Rydberg states? 2) At what values of principal quantum number and electronic angular momentum do different behaviors emerge for different species? 3) Does nuclear spin affect either electronic or rotational autoionization of Rydberg states into different ionic states? 4) Do spin interactions play a role in the relative branching ratio between ionization and dissociation in the decay of highly excited states? 5) What role does internuclear separation play in these spin dynamics? This project proposes to begin addressing these questions by investigating the structure and dynamics of highly excited molecular states, including the effects of orbital and rotational angular momentum and vibration on molecular spin interactions, by using the novel approach of time-resolved, resonant four-wave mixing spectroscopy. The goal is to perform high energy resolution measurements within a given Rydberg series or a given vibrational progression in order to follow the evolution of angular momentum coupling as a function of energy and internuclear separation. By examining three fundamental systems with distinct molecular structures; H2, N2 and the OH radical, prototypical interactions and dynamics can be systematically investigated. This kind of data, taken together with MQDT analyses, promises to provide new insights into the unique nuclear and electronic angular momentum interactions that molecules exhibit.