There is convincing evidence that the formation of complex organic molecules occurred in a variety of astrophysical environments. Among them, precursors of biomolecules are of particular significance due to their exobiological implications. Hexamethylenetetramine (HMT, C6H12N4) is one of these complex organic molecules of prime interest since its acid hydrolysis seems to form amino acids. It is also one of the main components of the organic residue formed from the warming of photolysed interstellar ice analogs. In the present work, the mechanism for HMT formation in interstellar or cometary ice analogs has been determined by combining laboratory experiments and DFT calculations. FTIR and mass spectrometry techniques have been used to follow experimentally the formation of HMT as well as its precursors from the warming of specific ice mixtures without irradiation.(1,2) The fruitful interplay between theory and experiment has allowed establishing the mechanism in solid state at low temperature. We show that HMT is thermally formed  from H2CO and NH3 activated by HCOOH. Two intermediates has been unambiguously detected: NH2CH2OH and the trimer of CH2NH (1,3,5-triazinane, TMT).(2) Unlike to what it was previously thought, HMT is not an indicator of ice photochemistry, but an indicator of thermal processing of ice.  Using kinetic data determined from this work, we could estimate the time of formation of HMT and of its intermediates in various astrophysical objects.  These results strengthen the hypothesis that HMT and its intermediates should be present in comets, where they may be detected with the COSAC or COSIMA instrument of the Rosetta mission.(1)(1) Vinogradoff et al. A&A (2013), 555, A13(2) Vinogradoff et al. P.C.C.P. (2012), 14, 12309

Formation of complex organic molecules in astrophysical ice analogs: A mechanistic approach

247th National Meeting (2014)

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