PHOTODISSOCIATION OF $NO^{+}$
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Date
1980
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Ohio State University
Abstract
$NO^{+}$ is the dominant ion in most regions of the ionosophere, yet almost all information on the many electronic states of this species has been obtained from photoelectron spectroscopy and form $theory.^{1}$ We observe predissociation of this ion to form $O^{+}$ and $N^{+}$ fragments over the wavelength region of 6500-5350 {\AA}. The measurements were made using the SRI laser-ion coaxial beams photofragment spectrometer with the ions produced by electron impact on NO gas. The observed transitions produce $N^{+}$ photofragments with kinetic energies of 0, 0.02, 0.3, and 0.4 eV and $O^{+}$ photofragments with 0.3, 0.4, 0.6, - 0.8, and 0.9 eV. The most extensive feature in these spectra is a system of 15 red-shaded bands observed at moderate ($0.8 cm^{-}1$) resolution between 6500-5700 {\AA} producing $O^{+}$ photofragments with kinetic energies between 0.6-0.8 ev. The variation of photofragment kinetic energy from band to band within this system demonstrates the transitions arise from two adjacent vibrational levels of a lower electronic state to 10 predissociated vibrational levels of an upper electronic state. The observed vibrational spacing of the lower state, together with the transition frequencies and photofragment kinetic energies, suggest the lower state is $b^{\prime}\ ^{3}\Sigma^{-}(v^{\prime\prime} =8,9)$. A strong perturbation is observed in the upper state vibrational spacing which is accompanied by a breaking-off of transitions from $v^{\prime\prime}=9$. The most likely candidate for this predissociated state is $c^{3}\pi$, which is expected to lie in the region of the observed photofragment energies and for which $theory^{2}$ predicts a double minimum. We have measured one of the vibrational bands in this system at high ($0.033 cm^{-1}$) resolution and find it composed of more than 280 discrete transitions whose narrow linewidths indicate a predissociation lifetime of $> 2$ ns. Rotational analysis of these data is in progress.
Description
$^{1}$D. L. Albritton, A. L. Schmeltekopf, and R. N. Zare, J. Chem. Phys. 71, 3271 (1979). $^{2}$P.W. Thulstrup, E. Thulstrup, A. Andersen, and Y. Ohrn, J. Chem. Phys. 60, 3975 (1974). Research supported by ARO and APOSR.
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