Methyl cyanide and propyne in the hot molecular core G34.3+0.15

CH3CN photochemistry at hot core margins

“…The observational details for CH 3 CN in the G34.3 UCHC are not quite encompassed by the shell model. Macdonald & Habing (1994) have reported a displacement of the CH 3 CN peak emission, observed by them with the Nobeyama Millimetre Array, relative to the NH 3 peak, observed with the Very Large Array (VLA) by Heaton, Little & Bishop (1989). The G34.3 hot core is offset slightly to the north of an axis of symmetry through the apex of the adjacent cometary ultra‐compact H ii (UCH ii) region.…”

“…The velocity difference between NH 3 and CH 3 CN, in addition to the displacement, is consistent with a flow of material parallel with the cometary `bow shock' front and compatible with recent observations of the larger scale dynamics of the G34.3 cloud (Gaume, Fey & Clausen 1994;Williams, Dyson & Redman 1996). The displacement was thought to fit a scenario in which NH 3 is evaporated from grains and processed within the flow into CH 3 CN over a time‐scale of ∼10 5 yr at a flow speed ∼1 km s −1 (Macdonald & Habing 1994; Millar, Macdonald & Habing 1995a,b). Unfortunately, while the earlier approximate calculations seemed to support this, the more detailed recent calculations of Millar et al (1997) do not.…”