An experimental study of the photodegradation of polyoxymethylene at 122, 147 and 193 nm

This paper presents results from a current experimental program whose aim i s to determine quantitatively the photochemical evolution of organic molecu les present or likely to be present in comets. Particularly, this includes the mechanisms involved in the degradation of high molecular weight compoun ds in cometary ices and dust, when they are submitted to photon bombardment in the surrounding area of the sun. Photodegradation of polyoxymethylene ( -CH2-O-),, is studied at 122, 147 and 193 nm. Experimental setup and analyt ical methods are presented (FTIR, GC-MS). We have identified the main gaseo us photodegradation products of polyoxymethylene: H2CO, CO, HCOOH, CO2, CH3 OH, CH3OCHO, CH3OCH3OCH3 and C3H6O3 (trioxane). We have determined the prod uction quantum yields for formaldehyde (Phi(122nm)=0.75+/-0.21, Phi(147nm)= 0.96+/-0.19) and formic acid (Phi(122nm)=0.13+/-0.05, Phi(147nm)=0.26+/-0.1 0), and roughly estimated the yields for the other compounds. Such data, th at were missing to interpret astronomical observations of comets, are now a vailable for further theoretical studies. We also propose mechanisms involv ed in the production of these molecules from polyoxymethylene. (C) 2000 Els evier Science S.A. All rights reserved.