  Observations with Cassini's Electron Spectrometer discovered negative ions in
Titan's ionosphere, at altitudes between 1400 and 950 km. Within the broad mass
distribution extending up to several thousand amu, two distinct peaks were
identified at 25.8-26.0 and 49.0-50.1 amu/q, corresponding to the carbon chain
anions $CN^-$ and/or $C_2H^-$ for the first peak and $C_3N^-$ and/or $C_4H^-$
for the second peak. In this study we present the spatial distribution of these
low mass negative ions from 28 Titan flybys with favourable observations
between 26 October 2004 and 22 May 2012. We report a trend of lower densities
on the night side and increased densities up to twice as high on the day side
at small solar zenith angles. To further understand this trend, we compare the
negative ion densities to the total electron density measured by Cassini's
Langmuir Probe. We find the low mass negative ion density and the electron
density to be proportional to each other on the dayside, but independent of
each other on the night side. This indicates photochemical processes and is in
agreement with the primary production route for the low mass negative ions
being initiated by dissociative reactions with suprathermal electron
populations produced by photoionisation. We also find the ratio of
$CN^-/C_2H^-$ to $C_3N^-/C_4H^-$ highly constrained on the day-side, in
agreement with this production channel, but notably displays large variations
on the nightside.
