Methyl formate (HCOOCH3) was first observed in the dense molecular cloud
Sgr B2 in 1975 by
Brown et al. and
Churchwell & Winnewisser
via a pair of rotational lines associated with the A and E
torsional states arising from the internal rotation of
the methyl group. Various later studies have found numerous other lines. Methyl formate was also identified in comet
gas phase formation pathways to interstellar methyl formate
cannot account for the observed
It is quite possible that grain surface reactions play an important role in the formation of methyl formate.
In addition to the low energy (~300 cm–1) barrier for rotation of the methyl
group, methyl formate has two distinct
isomers that are very close in energy but are separated by a barrier that is significant at
interstellar cloud temperatures. The figure shows a computed energy diagram for the structures where the
carbonyl O is on the same and opposite side
as the methyl group.