OH vibrational distributions: A comparison of Einstein [formula omitted] transition probabilities

Abstract

A limited number of studies have measured OH vibrational temperatures due in part to the difficulty of simultaneously observing multiple ro-vibrational emission bands. With questions still remaining about the quenching processes of the vibrationally excited OH molecule, observations of vibrational temperatures are critical to better characterize OH vibrational distributions. The Einstein A transition probabilities are a key element of OH population measurements, and their impact upon these observations have not been fully examined. The Perkins Airglow Study (PAS) is a spectroscopic survey of airglow emission and OH vibrational temperature, in the H-band, at a latitude of 35∘ N. The spectra have a resolution of r=λ/Δλ≈600, and employ a 10 s integration time. Airglow emission was continuously observed over the course of twenty entire nights, and the spectra contain emission from the OH(6-4), OH(5-3), OH(4-2), and OH(3-1) ro-vibrational bands. Currently PAS has recorded nearly 55,000 airglow spectra, and these observations significantly increase the current number of OH vibrational temperature measurements. The Einstein A coefficients examined in this work were found to have a significant impact upon the measured populations by nearly a factor of two. The observed OH vibrational temperatures averaged 10,500 K, and the Einstein A coefficients were found to vary the average measured vibrational temperature by 1,100 K.