Infrared laser spectroscopy of open-shell species

Abstract

In this thesis, infrared laser spectroscopy is employed to probe the structure and dynamics of open-shell molecular complexes in 0.4 K helium droplets. The Λ-doublet splittings of He-solvated OH radical in the ground and first excited vibrational states are determined to be 3.6 and 7.2 times larger than their respective gas phase values, and a model that assumes a realistic parity dependence of the effective moment of inertia reproduces the observed change quantitatively. The HOOO radical is produced via the association reaction between OH and O2. The ν1 and ν1+ν6 bands are found for the trans HOOO species, and no evidence for cis-HOOO or the weakly bound OH-O2 is observed. Stark spectroscopy of trans-HOOO reveals a large discrepancy between the measured dipole moments and the equilibrium values computed at the CCSD(T) complete basis set limit (CBS) level. When the CCSDT(Q)/CBS equilibrium dipole moments are adjusted for vibrational averaging, excellent agreement with experiment is obtained. The sequential addition of OH and multiple O2 molecules to helium droplets results in the formation of HO3-(O2)n clusters as large as n=4, and the spectra of these species are probed in the OH stretch region. For n=1, a comparison between the experimental result and ab initio calculations indicates a hydrogen-bonded 4A′ trans-HO3-O2 structure, consisting of a trans-HOOO core. Similarly, Al-(CO)n clusters (n≤5 ) are as-sembled in helium droplets. The rotationally resolved C-O stretch bands for 2Π1/2 Al-CO and 2B1 Al-(CO)2 complexes are observed. A broad band with pressure dependence of two CO molecules is found and tentatively assigned to the weakly bonded Al-CO-(CO) cluster. For the reaction between Al and HCN, a 2A′ bent-HCNAl species is found near 2690 cm-1. The σ donation and π donation between the Al atom and HCN ligand is investigated via a Natural Bond Orbital (NBO) analysis. These studies expand our understanding of the fundamental behavior of open-shell radical complexes in helium droplets.