  The composition of comets in the Solar System come in multiple groups thought
to encode information about their formation in different regions of the outer
protosolar disk. The recent discovery of the second interstellar object,
2I/Borisov, allows for spectroscopic investigations into its gas content and a
preliminary classification of it within the Solar System comet taxonomies to
test the applicability of planetesimal formation models to other stellar
systems. We present spectroscopic and imaging observations from 2019 September
20th to October 26th at the Bok, MMT, and LBT telescopes. We identify CN in the
comet's spectrum and set precise upper limits on the abundance of C2 on all
dates. We use a Haser model to convert our integrated fluxes to production
rates and find Q(CN) = 5.0 +/- 2.0 * 10^24 mol/s on September 20th and Q(CN) =
1.1 - 1.9 * 10^24 mol/s on later dates, both consistent with contemporaneous
observations. We set our lowest upper limit on a C2 production rate, Q(C2) <
1.6 * 10^23 mol/s, on October 10th. The measured ratio upper limit for that
date, Q(C2)/Q(CN) < 0.095 indicates that 2I/Borisov is strongly in the (carbon
chain) 'depleted' taxonomic group. The only comparable Solar System comets have
detected ratios near this limit, making 2I/Borisov statistically likely to be
more depleted than any known comet. Most 'depleted' comets are Jupiter Family
Comets, perhaps indicating a similiarity in formation conditions between the
most depleted of the JFCs and 2I/Borisov. More work is needed to understand the
applicability of our knowledge of Solar System comet taxonomies onto
interstellar objects, and we discuss future work that could help clarify the
usefulness of the approach.

Earth and Planetary Astrophysics