## Digitized Theses

1994

Dissertation

#### Degree Name

Doctor of Philosophy

#### Abstract

Observations of the hydroxyl airglow are widely used as a remote sensing tool in the study of middle atmosphere dynamics. To assess the validity of this technique, a comprehensive understanding of the excitation and emission processes is required. The effect of collisional quenching of vibrationally excited OH by {dollar}\rm O\sb2{dollar} remains an outstanding problem in interpreting OH airglow intensity variations. Impulsive collisions between {dollar}\rm OH\sp\*(\nu{dollar} = 1-9, K = 1,2,5,10) and {dollar}\rm O\sb2{dollar} are modelled using quasiclassical trajectories to investigate the distribution of product {dollar}\rm OH\sp\*{dollar} states. The mode of vibrational deactivation depends on whether the O or H atom is hit: V-T transfer results in the first case, V-R in the second case. The modelled quenching rates are inconsistent with measured rates of total removal from the vibrational levels via collisions with {dollar}\rm O\sb2{dollar}, indicating that the interaction is not well approximated by impulsive collisions for all vibrational levels. The similarity between the present results and highly excited rotational levels in the lower vibrational levels observed in the airglow support the possibility that impulsive collisions are occurring with another collision partner. In that case, the same mechanism that produces highly excited {dollar}K\sp{lcub}\prime\prime{rcub}{dollar} states from collisions with the H atom on OH may also produce significant single quantum quenching ({dollar}\Delta K \sim{dollar} 0) of the higher vibrational levels due to collisions with the O atom. The internal energy loss associated with these transitions is much greater than kT in the upper mesosphere. Therefore, there is some heating associated with this process.

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