Effects of N-Atom Concentration, Pressure, and Carrier Composition on Some First Positive Band Intensities in the Yellow Nitrogen Afterglow

Abstract

Absolute intensities of seven N₂ 1st positive bands with $\text{υ′\hspace{0.17em}=\hspace{0.17em}6–12}$ were measured as a function of carrier pressure, carrier composition, and N‐atom concentration in the range 4.5–0.06 torr. For an Ar carrier large pressure‐dependent shifts in the $B^3{\Pi }_g$ vibrational distribution to higher levels were observed below 4 torr; similar but much smaller shifts were also found for N₂ and He carriers. With Ar, reducing the N‐atom concentration shifted the vibrational distribution to lower levels. Changes in carrier composition produced large pressure dependent changes in the absolute and relative band intensities. An attempt was made to fit the results to a model involving vibrational relaxation and electronic quenching in $B^3\Pi$ . While qualitatively successful, this model could not account quantitatively for the observed relative intensity changes over the whole pressure range for which data are available and, in addition, implied physically unreasonable vibrational relaxation rates. It is suggested that the observed changes in the $B^3{\Pi }_g$ vibrational distribution below 4 torr may arise from vibrational relaxation in some precursor state.