  2I/Borisov - hereafter 2I - is the first visibly active interstellar comet
observed in the solar system, allowing us for the first time to sample the
composition of a building block from another system. We report on the
monitoring of 2I with UVES, the high resolution optical spectrograph of the ESO
Very Large Telescope at Paranal, during four months from November 15, 2019 to
March 16, 2020. Our goal is to characterize the activity and composition of 2I
with respect to solar system comets. We collected high resolution spectra at 12
different epochs from 2.1 au pre-perihelion to 2.6 au post perihelion. On
December 24 and 26, 2019, close to perihelion, we detected several OH lines of
the 309 nm (0-0) band and derived a water production rate of $2.2\pm0.2 \times
10^{26}$ molecules/s. The three [OI] forbidden oxygen lines were detected at
different epochs and we derive a green-to-red doublet intensity ratio (G/R) of
$0.31\pm0.05$ close to perihelion. NH$_2$ ortho and para lines from various
bands were measured and allowed us to derive an ortho-to-para ratio (OPR) of
$3.21\pm0.15$, corresponding to an OPR and spin temperature of ammonia of
$1.11\pm0.08$ and $31^{+10}_{-5}$ K, respectively. These values are consistent
with the values usually measured for solar system comets. Emission lines of the
radicals NH (336 nm), CN (388 nm), CH (431 nm), and C$_2$ (517 nm) were also
detected. Several FeI and NiI lines were identified and their intensities were
measured to provide a ratio of log (NiI/FeI) = $0.21\pm0.18$ in agreement with
the value recently found in solar system comets. Our high spectral resolution
observations of 2I/Borisov and the associated measurements of the NH$_2$ OPR
and the Ni/Fe abundance ratio are remarkably similar to solar system comets.
Only the G/R ratio is unusually high but consistent with the high abundance
ratio of CO/H$_2$O found by other investigators.
