The photodissociation of water in cometary atmospheres

Abstract

It is now known from laboratory and theoretical works that following water photodissociation, the OH radical is created in excited states of rotation or vibration. This fact was neglected in previous models of water photodissociation in cometary atmospheres. The goal of the present paper is to update these models. The water life time is not changed. The distribution of the OH ejection velocity, which has an average value (1.05 km/s) smaller than those given in previous studies is derived. The heating rate due to thermalization of the dissociation products is 3.3 x 10 to the -17th erg/s per water molecule. The emission of OH vibrational bands due to the creation of OH in excited vibrational states is evaluated. It is suggested that it could significantly contribute to the 'unidentified' feature observed at 2.8 microns in Comet Halley.