Spectroscopic measurements of non-equilibrium nitrogen plasmas at moderate pressures

Abstract

A local vibro-rotational analysis of the excited species, produced in a 35 MHz discharge reactor in flowing nitrogen, has been carried out by measuring radial and axial emission intensities of some vibrational sequences and selected rotational lines of the (0,2) band of the second positive system (SPS) of N 2 ( C 3Π u - B 3Π g ), in the pressure range 5–35 torr. Radial from lateral band or line emission intensities have been obtained by applying Abel's inversion technique to derive the corresponding vibrational and rotational temperatures with the use of Boltzmann plots. General maps of emission intensities and of vibrational and rotational temperature distributions within the reactor have been drawn. It is shown that a decrease of a factor 10 3 in the emission intensities from the core to the periphery of the discharge corresponds to a variation in T V and T R of only a factor ⋍2. This result has been interpreted on the basis of the kinetic mechanisms for the excitation and deexcitation of chemical species under discharge conditions. The decrease of V and the increase of T R with increasing pressure are interpreted according to V-R (vibration-rotation) energy-transfer mechanisms.