  We present strong detections of methyl cyanide, vinyl cyanide, ethyl cyanide
and cyanodiacetylene molecules with the Green Bank Telescope (GBT) toward the
Sgr B2(N) molecular cloud. Attempts to detect the corresponding isocyanide
isomers were only successful in the case of methyl isocyanide for its
J(K)=1(0)-0(0) transition, which is the first interstellar report of this line.
To determine the spatial distribution of methyl isocyanide, we used archival
Berkeley-Illinois-Maryland Association (BIMA) array data for the J(K)=4(K)-3(K)
(K=0-3) transitions but no emission was detected. From ab initio calculations,
the bonding energy difference between the cyanide and isocyanide molecules is
>8500 cm^-1 (>12,000 K). That we detect methyl isocyanide emission with a
single antenna (Gaussian beamsize(Omega_B)=1723 arcsec^2) but not with an
interferometer (Omega_B=192 arcsec^2), strongly suggests that methyl isocyanide
has a widespread spatial distribution toward the Sgr B2(N) region. Thus,
large-scale, non-thermal processes in the surrounding medium may account for
the conversion of methyl cyanide to methyl isocyanide while the LMH hot core,
which is dominated by thermal processes, does not produce a significant amount
of methyl isocyanide. Ice analog experiments by other investigators have shown
that radiation bombardment of methyl cyanide can produce methyl isocyanide,
thus supporting our observations. We conclude that isomers separated by such
large bonding energy differences are distributed in different interstellar
environments, making the evaluation of column density ratios between such
isomers irrelevant unless it can be independently shown that these species are
co-spatial.
