The effect of vibration-rotation interaction on intensity measurements of OH in shock tubes

Abstract

Recent intensity measurements of emission from the OH 2 Σ → 2Π system at temperatures near 3500°K in a shock tube have been utilized to yield spectroscopic temperatures and absorption oscillator strengths (1, 2). The shock tube data were reduced on the assumption of negligible vibration-rotation interaction. Calculations based on the Franck-Condon factors given by Learner (3) are presented here to show that the effect of vibration-rotation interaction is negligible and that this assumption is therefore valid for the conditions of the shock tube experiments. Results show that near 3500°K the spectroscopic temperatures based on emission from the (0, 0)-, (1, 1)-, (2,2)-, and (3, 3)-bands would be increased by vibration-rotation interaction about 70°K, which is within the estimated experimental error of ±75°K. The vibration f-number data of reference 2 (which is based on emission from the (0,0)-band only) is affected by less than 0·4 per cent up to 5000°K when assuming vibration-rotation interaction.