Spectroscopy of Reactive Molecules and Clusters

Citation

Johnson, Matthew Stanley (1996) Spectroscopy of Reactive Molecules and Clusters. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/ta23-4185. https://resolver.caltech.edu/CaltechTHESIS:04202020-161109407

Abstract

This thesis presents spectroscopic investigations of reactive molecules and clusters. The techniques of laser excited fluorescence, infrared predissociation spectroscopy, and photoelectron spectroscopy were employed to investigate systems relating to fundamental cluster chemistry, ion solvation, and atmospheric ozone depletion.

An instrument was developed to investigate van der Waals complexes of refractory elements. A pulsed laser ablation cluster source harnessed the cooling power of a supersonic free jet to condense weakly bound neutral clusters. Laser excited fluorescence was used to characterize the products of the source, which included adducts of aluminum atoms with water molecules, hydrogen, and argon. The species Al(H₂O), AlAr and AlH were identified.

The infrared predissociation spectra of positive and negative cluster ions were investigated using a tandem time-of-flight instrument. In this work the photofragment yield spectrum of mass-selected I⁻(H₂O) and I⁻(H₂O)₂ complexes was measured between 3170 and 3800 cm⁻¹. The dominant features in the I⁻(H₂O) spectra were assigned as a hydrogen bonded OH stretch and a free OH stretch. Ab initio calculations were used to aid in spectral assignment and for geometrical information concerning I⁻(H₂O). Absorptions in the iodide water dimer cluster are attributed to a symmetric and an antisymmetric bonded OH stretch, and a free OH stretch.

Chlorine nitrate is a key reservoir of stratospheric chlorine, and as such its photolysis branching ratio is crucial to partitioning of species involved with stratospheric ozone depletion. The He(I) photoelectron spectrum of chlorine nitrate was measured and assigned in order to understand the photodissociation behavior of chlorine nitrate. The results include the ionization potential of the molecule (10.86 eV), and the assignment of the first ionization peak to a nonbonding chlorine atomic orbital.

Thesis Files