SEMAPh.Or.E COMETAIRE, a tool for the study of the photochemical decomposition of probable large organic molecules in comets. First application: Polyoxymethylene

This paper presents a current experimental program concerning the study of the photochemical evolution of the organic matter ejected from the cometary nucleus. The aim of the work is to better understand, using laboratory sim ulations, the mechanisms which are involved in the degradation of the high molecular weight organics in cometary ices and dust when they are submitted to the warming up and to the bombardment of photons in the surrounding are a of the Sun. This experimental study will establish correlations between t he nucleus and the molecular composition of the coma. Furthermore, experime ntal data will provide useful information to bring to a close the question of the origin of the extended sources of H2CO and CO. Polyoxymethylene, sus pected to be present in the cometary nucleus, is often mentioned as a possi ble parent molecule for the extended source of H2CO. In order to test this hypothesis, irradiation of POM has been performed at 147 nm. The preliminar y results show effectively H2CO as one photodegradation product as well as CO, CO2 and HCOOH. Tentative detections of CH3OCH3, CH3OCH2OCH3, CH3OCHO an d C3H6O3 are also presented. (C) 1999 Elsevier Science Ltd. All rights rese rved.