Abstract

Two monochromatic pictures of the Comet Kohoutek (1973f) were taken on January 15, 1974 in the resonance light (A² - X² ) of the radical OH with a photographic telescope placed on board the NASA 990 Convair airplane. From an intensity profile we derive the production rate of OH radicals Q_OH = 4 xsx 10²⁸ moleculesec ^-1sr^-1 at 0.6 AU and the lifetime of the OH radical which is _OH = 4.5 × 10⁴ sec at 0.6 AU. This short lifetime (very similar to the lifetime of H₂O) combined with the high total production rate of gas in comets can explain the observed velocity of 8km sec^-1 for the H-atoms: The H-atoms produced by photodissociation of H₂O are thermalized at short distancesfrom the nucleus; the H-atoms produced by photodissociation of OH have a velocity of 8km sec^-1 and can reach the outer part of the hydrogen envelope.