INDUCED INFRARED ABSORPTION OF NITROGEN AND NITROGEN – FOREIGN GAS MIXTURES

Abstract

The pressure-induced fundamental vibration–rotation absorption band of nitrogen was studied in the pure gas and in nitrogen–argon, nitrogen–hydrogen, and nitrogen–helium mixtures at room temperature for pressures up to 1 500 atm. The shapes of the absorption profiles obtained in each case were discussed. The enhancement absorption profiles of nitrogen–argon mixtures exhibited the sharpening of the individual branches of the fundamental band with a small frequency shift, while those of nitrogen–hydrogen and nitrogen–helium mixtures indicated a splitting of the Q branch. Binary and ternary absorption coefficients were determined for pure nitrogen and nitrogen – foreign gas mixtures. The graph drawn with (1/ρ_a²) ∫α(ν)dν vs. ρ_a for pure nitrogen and those drawn with (1/ρ_aρ_b) (∫α(ν)dν)_enhancement vs. ρ_b for mixtures were found to be straight lines. Except for nitrogen–helium mixtures all these straight lines had negative slopes, and this was interpreted as a partial cancelation of the induced moments due to ternary collisions. Applying the theory of Van Kranendonk and using the known molecular constants, the molecular quadrupole moment Q of nitrogen and its derivative Q′ with respect to the internuclear distance at its equilibrium position were determined. The values of Q and Q′ were obtained as 1.1ea₀² and 0.97ea₀ respectively; the value of Q is in good agreement with that determined by previous investigators.