  We introduce a simulation framework for the transport of high and low energy
electrons in xenon-based gaseous optical time projection chambers (OTPCs). The
simulation relies on elementary cross sections (electron-atom and
electron-molecule) and incorporates, in order to compute the gas scintillation,
the reaction/quenching rates (atom-atom and atom-molecule) of the first 41
excited states of xenon and the relevant associated excimers, together with
their radiative cascade. The results compare positively with observations made
in pure xenon and its mixtures with CO$_2$ and CF$_4$ in a range of pressures
from 0.1 to 10~bar. This work sheds some light on the elementary processes
responsible for the primary and secondary xenon-scintillation mechanisms in the
presence of additives, that are of interest to the OTPC technology.

Instrumentation and Detectors