  The Cassini Plasma Spectrometer (CAPS) Electron Spectrometer (ELS) instrument
onboard Cassini revealed an unexpected abundance of negative ions above 950 km
in Titan's ionosphere. \textit{In situ} measurements indicated the presence of
negatively charged particles with mass-over-charge ratios up to 13,800
\textit{u/q}. At present, only a handful of anions have been characterized by
photochemical models, consisting mainly of C$_n$H$^-$ carbon chain and
C$_{n-1}$N$^-$ cyano compounds ($n=2-6$); their formation occurring essentially
through proton abstraction from their parent neutral molecules. However,
numerous other species have yet to be detected and identified. Considering the
efficient anion growth leading to compounds of thousands of \textit{u/q}, it is
necessary to better characterize the first light species. Here, we present new
negative ion measurements with masses up to 200 \textit{u/q} obtained in an
\ce{N2}:\ce{CH4} dusty plasma discharge reproducing analogous conditions to
Titan's ionosphere. We perform a comparison with high altitude CAPS-ELS
measurements near the top of Titan's ionosphere from the T18 encounter. The
main observed peaks are in agreement with the observations. However, a number
of other species (\textit{e.g.} \ce{CNN-}, \ce{CHNN-}) previously not
considered suggests an abundance of N-bearing compounds, containing two or
three nitrogen atoms, consistent with certain adjacent doubly-bonded nitrogen
atoms found in tholins. These results suggest that an N-rich incorporation into
tholins may follow mechanisms including anion chemistry, further highlighting
the important role of negative ions in Titan's aerosol growth.
