  Comet C/2016 R2 (PanSTARRS) has a peculiar volatile composition, with CO
being the dominant volatile as opposed to H$_2$O and one of the largest
N$_2$/CO ratios ever observed in a comet. Using observations obtained with the
\textit{Spitzer Space Telescope}, NASA's Infrared Telescope Facility, the
3.5-meter ARC telescope at Apache Point Observatory, the Discovery Channel
Telescope at Lowell Observatory, and the Arizona Radio Observatory 10-m
Submillimeter Telescope we quantified the abundances of 12 different species in
the coma of R2 PanSTARRS. We confirm the high abundances of CO and N$_2$ and
heavy depletions of H$_2$O, HCN, CH$_3$OH, and H$_2$CO compared to CO reported
by previous studies. We provide the first measurements (or most sensitive
measurements/constraints) on H$_2$O, CO$_2$, CH$_4$, C$_2$H$_6$, OCS,
C$_2$H$_2$, and NH$_3$, all of which are depleted relative to CO by at least
one to two orders of magnitude compared to values commonly observed in comets.
The observed species also show strong enhancements relative to H$_2$O, and even
when compared to other species like CH$_4$ or CH$_3$OH most species show
deviations from typical comets by at least a factor of two to three. The only
mixing ratios found to be close to typical are CH$_3$OH/CO$_2$ and
CH$_3$OH/CH$_4$. While R2 PanSTARRS was located at a heliocentric distance of
2.8 AU at the time of our observations in January/February 2018, we argue that
this alone cannot account for the peculiar observed composition of this comet
and therefore must reflect its intrinsic composition. We discuss possible
implications for this clear outlier in compositional studies of comets obtained
to date, and encourage future dynamical and chemical modeling in order to
better understand what the composition of R2 PanSTARRS tells us about the early
Solar System.
