ULTRAVIOLET LASER INDUCED FLUORESCENCE SPECTROSCOPY OF MOLECULAR IONS IN A RADIOFREQUENCY ION TRAP
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Date
1983
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Ohio State University
Abstract
The application of laser induced fluorescence spectroscopy to measure electronic spectra of molecular ions confined in a radiofrequency ion trap was pioneered by Mahan and co-$workers,^{1}$who used visible lasers to study LIF spectra of $CH^{+}$, $CO^{+}$, ${N_{2}}^{+}$, $BrCN^{+}$, $H_{2}S^{+}$, hexafluorobenzene, and 1,3,5-trifluorobenzene cations. We have emended this technique into the ultraviolet (218-350 nm) through the use of a Nd-YAG-pumped dye laser system with nonlinear crystals permitting frequency doubling and mixing with the YAG-fundamental. The 0,0 band of the $A^{2}\sum^{+} -X^{2}\sum\nolimits^{+}$ system of $CO^{+}$ was observed at wavelengths near 219 nm. These measurements were obscured by the presence of a continuous background fluorescence, that varied approximately as the cube of the ultraviolet intensity. This as yet unidentified non-linear background was minimized by operating at the lowest laser powers that produced detectable A-X fluorescence. The 1,3 band of the similar $B^{2}\sum^{+}-X^{2}\sum^{+}$ transition of ${N_{2}}^{+}$ was recorded near 330 nm. The 0,0 and 1,0 bands of the $A^{2}\sum\nolimits^{+} -X^{2}\Pi_{3/2}$ systems of $HC1^{+}$ and $HBr^{+}$ were recorded near 350 nm and 330 nm, respectively. Rotational state-resolved radiative lifetimes were measured for low-J states of each ion. No J-variation in the lifetimes is apparent. For $HCl^{+}$, $\tau = 3.2 \pm .4$ and for $HBr^{+} \tau= 3.9 \pm .2$, in reasonable agreement with measurements of unresolved vibronic $bands.^{1}$ F. J. Grieman, B. H. Mahan, A. O’Keefe, and J. S. Winn, Faraday Disc. 71, 191 (1981). $^{*}$ Supported by NSF Grant \# CHE 8207307.""
Description
Author Institution: Department of Chemistry, University of California