THE $4s \leftarrow 3p$ ELECTRONIC TRANSITION IN ALUMINUM ATOM-MOLECULE COMPLEXES: BOUND AND REPULSIVE EXCITED STATES
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Date
2001
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Ohio State University
Abstract
An investigation of the $4s \leftarrow 3p$ electronic transition in weakly bound binary complexes of the Al atom with Ne and several molecules ($H_{2}$, $D_{2}$, $N_{2}$, $CH_{4}$) is reported. In contrast with the higher excited Al atomic states where the interactions are all attractive, the observed spectra are indicative of both attractive and repulsive interactions of Al(4s) with these partners. No fluorescence was detected upon laser excitation of this electronic transition in the $Al-N_{2}$ and $Al-CH_{4}$ complexes. Fluorescence depletion spectroscopy, using the $3d \leftarrow 3p$ electronic transition as the probe transition, was employed to observe these transitions. The $4s \leftarrow 3p$ transitions in $Al-N_{2}$ and $Al-CH_{4}$ show vibrational structure, assigned as an excitedstate progression in the van der Waals stretch mode. An unstructured feature to the blue of the Al $4s \leftarrow 3p$ atomic transition was observed in the laser fluorescence excitation spectra of the $AlNe$, $Al-H_{2}$, and $Al-D_{2}$ complexes. These spectra are a consequence of the repulsive nature of the interaction of Al(4s) with these partners, as in the corresponding isovalent complexes involving boron. With the availability of an ab initio potential energy curve for the ground state, a potential energy curve for the excited $AlNe(B^{2}\Sigma^{+})$ electronic state was derived by a fit to the observed AlNe excitation spectrum.
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Author Institution: The Johns Hopkins University; Department of Chemistry, The Johns Hopkins University