THE HIGH RESOLUTION SPECTRUM OF THE SECOND POSITIVE BAND SYSTEM OF $N_{2}$ UNDER ELECTRON BEAM EXCITATION

The high resolution spectrum of the second positive band system of $N_{2}$ has been recently reinvestigated by Venkateswarlu, Murthy and Basu using a transversely excited segmented electrode nitrogen laser tube just below and just above laser threshold. In the present work, nitrogen at a pressure of 3 torr was excited by a Febetron 706 electron beam (400 KeV) generator using 3 ns pulses. Spectra were taken using a vacuum Ebert spectrograph in the 17th and 18th orders at dispersion of about $ 0.1A^{\\circ}$/mm. The rotational structure of the 0-0, 0-1 and 1-0 laser bands has been studied. More R branch lines are found to lase than those recorded earlier. Mixtures of $N_{2}$ and He at relative pressures of 3-10 torr of $N_{2}$ and 10 to 20 torr of He have been excited with the electron beam to study selective excitations in the rotational spectrum. It was found that the rotational 1ine $Q_{3}$ (2) lases at the expense of the line $R_{3}$ (4). The energy separation between the lower levels $J = 4$ and $J = 2$ of these lines is about $25 cm^{-1}$ which corresponds to the separation between 13s $^{1}S$ and $^{3}S$ of He suggestion an energy transfer between He and $N_{2}$ to be responsible for the selective excitation of $Q_{3}$ (2) over $R_{3}$ (4). 1. P. Venkateswarlu, A. N. Murthy and S. K. Basu, Ind. J. Phys., 54B, 388 (1980)