  Volatile organic emissions were detected post-perihelion in the long period
comet C/2006 M4 (SWAN) in October and November 2006. Our study combines
target-of-opportunity observations using the infrared Cryogenic Echelle
Spectrometer (CSHELL) at the NASA-IRTF 3-m telescope, and millimeter wavelength
observations using the Arizona Radio Observatory (ARO) 12-m telescope. Five
parent volatiles were measured with CSHELL (H2O, CO, CH3OH, CH4, and C2H6), and
two additional species (HCN and CS) were measured with the ARO 12-m. These
revealed highly depleted CO and somewhat enriched CH3OH compared with
abundances observed in the dominant group of long-period (Oort cloud) comets in
our sample and similar to those observed recently in Comet 8P/Tuttle. This may
indicate highly efficient H-atom addition to CO at very low temperature (~ 10 -
20 K) on the surfaces of interstellar (pre-cometary) grains. Comet C/2006 M4
had nearly "normal" C2H6 and CH4, suggesting a processing history similar to
that experienced by the dominant group. When compared with estimated water
production at the time of the millimeter observations, HCN was slightly
depleted compared with the normal abundance in comets based on IR observations
but was consistent with the majority of values from the millimeter. The ratio
CS/HCN in C/2006 M4 was within the range measured in ten comets at millimeter
wavelengths. The higher apparent H-atom conversion efficiency compared with
most comets may indicate that the icy grains incorporated into C/2006 M4 were
exposed to higher H-atom densities, or alternatively to similar densities but
for a longer period of time.
