Possible gas-phase syntheses for seven neutral molecules studied recently with the Green Bank Telescope

Abstract

Aims. With the Green Bank telescope (GBT), seven neutral molecules have been newly detected or confirmed towards either the cold interstellar core TMC-1 or the hot core source Sgr B2(N) within the last 1–2 years. Towards TMC-1, the new molecules seen are cyanoallene (CH2CCHCN) and methyl triacetylene (CH3C6H) while methyl cyanoacetylene (CH3CCCN) and methyl cyanodiacetylene (CH3C5N) were confirmed. Towards Sgr B2(N), the three newly detected molecules are cyclopropenone (c-C3H2O), ketenimine (CH2CNH), and acetamide (CH3CONH2); these are mainly seen in absorption and are primarily located in an envelope around the hot core. In this work, we report a detailed study of the gas-phase chemistry of all seven molecules. Methods. Starting with our updated gas-phase chemical reaction network osu.01.2007, we added formation and depletion reactions to treat the chemistry of each of the seven molecules. Some of these were already in our network but with incomplete chemistry, while most were not in the network at all prior to this work. We assumed the standard physical conditions for TMC-1 and assumed that these also hold for the envelope around Sgr B2(N). Standard pseudo-time-dependent calculations were run for each source. Results. For TMC-1, we reproduced the observed fractional abundances of three detected molecules at early times of 10 5−6 yr and came close to reproducing a fourth. For the halo surrounding Sgr B2(N), our results are more ambiguous: only for ketenimine were we able to match the observed abundance very well.