SPECTRA AND STRUCTURE OF THE $W^{3}\Delta_{u}$ STATE OF $N_{2}$
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Date
1970
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Ohio State University
Abstract
The $W^{3}\Delta_{u}$ state of $N_{2}$ has been identified in two band systems of $N_{2}$, the $W^{3}\Delta_{u}\mathop{\rightarrow}\kern -10pt_{\leftarrow} B^{3}\Pi_{g}$ transition in emission falling wholly in the infrared (and produced most readily between 2 and 4.5 microns), and a recently identified ultraviolet absorption system, W $^{3}\Delta_{u}\leftarrow X^{1}\Sigma^{+}_{g}$. Fifteen bands have been observed in the permitted infrared system and three in the forbidden ultraviolet system. At the available resolution of about $0.5 cm^{-1}$, the rotational structure of the infrared bands was not well resolved. Accordingly, computer generated bands, based on individual line intensities calculated by Kovacs and Toros for a $^{3}\Delta-^{3}\Pi$ transition, were used as models for the recorded infrared spectra. The lines are weighted as to relative population, smeared as by the spectrometer and summed to generate the ordinates for a computer plot. Comparing the generated bands to the measured bands leads to specification of the band origins and, parametrically, to the rotational constants for the W $^{3}\Delta_{u}$ state. By combining the available information from both the infrared and ultraviolet systems, an improved set of vibrational constants has been calculated for the W $^{3}\Delta_{u}$ state. The v=0 level of the W $^{3}\Delta_{u}$ state is metastable (the v=1 less so) and could become significantly populated in certain collisionless environments, such as the upper atmosphere. This level then becomes a candidate for the upper state of a progression of bands terminating in the ground state, X $^{1}\Sigma^{+}_{g}$. Emission intensities are calculated for this transition and compared with available auroral spectra.
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Author Institution: Institute for Molecular Physics, University of Maryland