  We aimed to study the chemistry of the circumnuclear molecular gas of
NGC1068, and to compare it with those of the starburst galaxies M82 and NGC253.
Using the IRAM-30m telescope, we observed the inner 2 kpc of NGC1068 between
86.2 GHz and 115.6 GHz. We identified 35 spectral features, corresponding to 24
different molecular species. Among them, HC3N, SO, N2H+, CH3CN, NS, 13CN, and
HN13C are detected for the first time in NGC1068. Assuming local thermodynamic
equilibrium (LTE), we calculated the column densities of the detected
molecules, as well as the upper limits to the column densities of some
undetected species. The comparison among the chemistries of NGC1068, M82, and
NGC253, suggests that, apart from X-rays, shocks also determine the chemistry
of NGC1068. We propose the column density ratio between CH3CCH and HC3N as a
prime indicator of the imprints of starburst and AGN environments in the
circumnuclear interstellar medium. This ratio is, at least, 64 times larger in
M82 than in NGC1068, and, at least, 4 times larger in NGC253 than in NGC1068.
Finally, we used the UCL_CHEM and UCL_PDR chemical codes to constrain the
origin of the species, as well as to test the influence of UV radiation fields
and cosmic rays on the observed abundances.
