HIGH RESOLUTION NEAR-INFRARED SPECTRUM OF THE $N_{2}^{+}$ MEINEL SYSTEM, $A\ ^{2}\Pi_{ui} \to X\ ^{2}\Sigma_{g}^{+}$
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Date
1979
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Ohio State University
Abstract
Spectroscopic evidence for the existence of the first excited state, $A^{2}\Pi_{u}$, of the nitrogen molecular iron first came from the observation of perturbations in the First Negative band system $(B^{2}\Sigma^{+}_{u} \rightarrow \chi ^{2}\Sigma^{+}_{g})$ of $N_{2}^{+}$. The $A ^{2}\Pi_{u} \rightarrow \chi ^{2}\Sigma^{+}_{g}$ band system was observed by Meinel in the $aurora,^{1}$ and, accordingly, given his name. The system extends into the infrared with the 0-0 band appearing near 11100$\AA$. Laboratory studies on this system were undertaken by Douglas working at high resolution in the photographic infrared. The present investigation has been carried out photometrically. Cooled photomultipliers were used up to the 1-0 band at 9200{\AA} and a cooled intrinsic germanium photodiode permitted observation of the 0-0 band. The spectra were obtained using a specialized hollow cathode source and a 5-meter Jarrell-Ash spectrograph adapted to spectrometric operation through the installation of an exit slit translated with a lead screw assembly driven by a stepping motor. For the 0-0 band, the arrangement leads to a plate factor of 0.6 {\AA}/mm in fifth order, a resolving power of $0.05 cm^{-1}$, and a wavenumber precision of $0.01 cm^{-1}$. The investigation encompasses a dozen bands emanating from the vibrational levels $\nu = 0$ to 5 and rotational levels N = 1 to 26 of the $A^{2}\Pi_{u}$ state. The data permits the calculation of improved spectroscopic constants for all of the participating levels of the $A^{2}\Pi_{u}$. Of particular interest are the origins of the 0-0 and 1-0 bands which specify the bottom of the $A^{2}\Pi_{u}$ potential curve and which have not previously been subject to direct measurement.
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$^{1}$ A. B. Meinel, Astrophys. J. 112 562-563 (1950). $^{2}$ A. E. Douglas, Astrophys. J. 117 380-386 (1953). This research was supported, in part, by the Atmospheric Sciences Section, NSF and by the Chemistry Section, NSF.
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