Free Jet Expansion Laser Spectroscopy of van der Waals Molecules Containing Ne and Br₂

Author: Swartz, Barry Allan

Year: 1984

Degree: Dissertation (Ph.D.)

Advisor: Sparks, Randal K.

Committee Members: Janda, Kenneth C.; Dervan, Peter B.; McGill, Thomas C.; Sparks, Randal K.

Option: Chemistry

DOI: 10.7907/mp06-am61

Abstract

Fluorescence excitation spectra of complexes of Ne and Br2 containing up to four Ne atoms have been measured. The van der Waals molecules were synthesized in a free jet expansion and excited with tunable excimer-pumped dye laser radiation. Features attributable to van der Waals complexes by virtue of their intensity dependences on molecular beam stagnation pressure appear shifted to the blue of band origins of the B3Πo+g ← X1Σ+g transition of all three isotopic species of Br2. Spectra were recorded for transitions (11-0) through (30-0) of Br2 which show that the specral shifts of the complexes relative to the Br2 band origins increase with increasing v'. NeBr2 shifts range from 5.5 to 8.8 cm-1. The spectral widths of the van der Waals features also increase with v' from a laser bandwidth limited value of 0.10 cm-1 for NeBr2 (16-0) to 3.1 cm-1 for (27-0). This indicates a greater than order of magnitude change in the lifetimes of these complexes with level of vibrational excitation which is disucssed in relation to recent theories on the dynamics of weakly bound systems. Estimates of 73 and 64 cm-1 were obtained for the van der Waals bond dissociation energy for the ground and excited electronic states, respectively.

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