The degree of coupling between free electron and nitrogen vibrational temperatures in weakly ionized nozzle expansions of shock-heated nitrogen has been determined. Free electron temperatures were measured with Langmuir probes while nitrogen vibrational temperatures were determined with a new instrument based on the electron beam technique. The resultant data were analytically correlated by coupling chemical nonequilibrium with nitrogen vibrational and free electron temperature nonequilibrium. It was found that a vibrational loss factor of 7 × 10−4 and an effective translational-rotational loss factor of 4.26 × 10−4 best predicted the measured electron temperature distributions.

Nomenclature vibrational term value in 7V 2 ground state intensity of rotational line emission intensity of vibrational band emission rotational quantum number number density of N 2 rotational state sum vibrational state sum Franck-Condon factor for excitation (N 2 A" 1 rotational temperature vibrational temperature vibrational quantum number characteristic rotational temperature Superscripts ( )' = quantities for excited electronic state of N 2 + (£ 2 2) ( Y = quantities for ground electronic state of N 2 + (X 2 2) Subscripts ( ) 0 = quantities for ground electronic state of N 2 (X 1^)I N recent years, the electron beam diagnostic technique has emerged as one of the more promising methods for examining low-density flowfields. In this technique, a narrow beam of electrons is projected across the flow, and the interaction of the electrons with gas particles produces a thin column of radiating gas nearly coincident with the beam. Spectroscopic analysis of the radiation yields a direct measurement of the rotational and vibrational temperatures and concentrations of the active species at arbitrary locations within the test gas. The technique is particularly attractive because the beam has no measurable influence on the basic energy state of the test gas and can be applied to any lowdensity flow regardless of the gasdynamic, chemical, and thermodynamic nature of the effluent.Analyses of the spectra induced by an electron beam passing through both nitrogen and air flows have been presented by various authors. 1 ~6 In addition, experimental studies have substantiated the over-all validity of the beam technique. 1 -2 Many details of the procedures to be employed in temperature determination are available, particularly in Refs. 1 and 2. However, little regard has been given to the effect of elevated rotational and vibrational temperatures on the measurement of species concentrations. It is the purpose of this note to point out the detailed influence of these elevated temperatures and to present techniques that can be employed for concentration measurements with varying degrees of rotational and vibrational excitation.When an electron beam with energies in the range of 10 to 20 kev is passed through either air or molecular nitrogen, the predominant radiation is due to the first negative emission system of N 2 + . The most intense band in the emission is the (0,0) band at 3914 A. Spectra from other species present in heated air (NO, 0 2 , 0) have been observed, 7 but with intensities much less than that of the N 2 + (0,0) band. In the following, reference is made only to the properties of molecular nitrogen.

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