Spectroscopic investigations of the X and A state dynamics of ¹³C₂H₂

Abstract

The objective of the experiments described in this thesis is to perform a detailed spectroscopic study of the dynamics on the A and X state surfaces of 13C2H2 in order to further understand the acetylene - vinylidene isomerization process in the ground electronic state. Acetylene exemplifies one of the simplest bond-breaking isomerization systems and it has served as a prototype for studies of large amplitude vibrational motion in molecules. The short-time, large amplitude, vibrational dynamics of acetylene are well understood up to the acetylene - vinylidene isomerization barrier. However, direct observation of acetylene - vinylidene isomerization remains elusive. To this end, five experimental techniques, Laser Induced Fluorescence (LIF), Dispersed Fluorescence (DF), Cavity Ring-Down Spectroscopy (CRDS), Noise Immune Cavity Enhanced Optical Heterodyne Molecular Spectroscopy (NICE-OHMS) and Stimulated Emission Pumping (SEP) are employed to study the spectroscopy and dynamics of acetylene. All of these experiments focus on 13C2H2 instead of 12C2H2, except for the Cavity Ring-Down measurements. These experiments concentrate on 13C2H2 because of the possibility of observing nuclear permutation tunneling splittings which are indicative of acetylene - vinylidene isomerization. The experiments described here provide the necessary foundation for observing nuclear permutation tunneling splittings. Attempts were made to observe nuclear permutation tunneling splittings in 13C2H2 using NICE-OHMS and SEP. Although permutation splittings were not observed, these experiments enhanced our knowledge of the dynamics and spectroscopy of the A and X states of 13C2H2.

(cont.) Moreover, these experiments have led to a better understanding of how to design and focus future studies in order to successfully observe nuclear permutation tunneling splittings in 13C2H2 as a means for directly observing acetylene - vinylidene isomerization.