The Production and Potential Detection of Hexamethylenetetramine-Methanol in Space

Numerous laboratory studies of astrophysical ice analogues have shown that their exposure to ionizing radiation leads to the production of large numbers of new, more complex compounds, many of which are of astrobiological interest. We show here that the irradiation of astrophysical ice analogues containing H₂O, CH₃OH, CO, and NH₃ yields quantities of hexamethylenetetramine-methanol (hereafter HMT-methanol; C₇N₄H₁₄O) that are easily detectible in the resulting organic residues. This molecule differs from simple HMT, which is known to be abundant in similar ice photolysis residues, by the replacement of a peripheral H atom with a CH₂OH group. As with HMT, HMT-methanol is likely to be an amino acid precursor. HMT has tetrahedral (T) symmetry, whereas HMT-methanol has C symmetry. We report the computed expected infrared spectra for HMT and HMT-methanol obtained using ab initio quantum chemistry methods and show that there is a good match between the observed and computed spectra for regular HMT. Since HMT-methanol lacks the high symmetry of HMT, it produces rotational transitions that could be observed at longer wavelengths, although establishing the exact positions of these transitions may be challenging. It is likely that HMT-methanol represents an abundant member of a larger family of functionalized HMT molecules that may be present in cold astrophysical environments.