Shock-Tube Study of the Vibrational Relaxation of Nitrogen Using Vacuum-Ultraviolet Light Absorption

The results of a shock-tube study of the vibrational relaxation of nitrogen over the approximate temperature range 3000° to 9000°K are presented. Measurements were made using a vacuum-ultraviolet light-absorption technique at 1176 Å which monitored the rate of populating vibrational level v″≃10. The good agreement of the present results with earlier interferometric measurements demonstrates the validity of the assumption that the populations of vibrational levels from the ground state up to at least v″ = 10 relax via a continuous sequence of ``near'' Boltzmann distributions which are described by a single time-dependent vibrational temperature. At temperatures in excess of about 5500°K, where no shock-tube data have previously been reported, the results indicate that the local value of the characteristic vibrational relaxation time becomes increasingly dependent on the degree of vibrational excitation, such that it decreases within the relaxation region as equilibrium is approached.