Photodegradation of hexamethylenetetramine by VUV and its relevance for CN and HCN extended sources in comets

This paper presents our first experimental results on the photodegradation at 147 and 122 nm of hexamethylenetetramine (HMT). This molecule, suspected to be present on cometary grains, could be responsible for extended sources of CN and HCN in comets. We show that if HMT is quite resistant to direct photolysis under vacuum, interactions with water vapor photoproducts, which could happen in inner comae, lead to a much more efficient degradation with formation of HCN, NH3 and other N bearing molecules. Thus HMT could act as a parent or grand parent molecule for observed extended sources. However, additional source with greater degradation efficiency is certainly required to account observations in outer comae. [Copyright &y& Elsevier]