  The dissociation of CO2 molecules in plasmas is a subject of enormous
importance for fundamental studies and the recent interest in carbon capture
and carbon-neutral fuels. The vibrational excitation of the CO2 molecule plays
an important role in the process. The complexity of the present state-to-state
(STS) models makes it difficult to find out the key parameters. In this paper
we propose as an alternative a numerical method based on the diffusion
formalism developed in the past for analytical studies. The non-linear
Fokker-Planck equation is solved by the time-dependent diffusion Monte Carlo
method. Transport quantities are calculated from STS rate coefficients. The
asymmetric stretching mode of CO2 is used as a test case. We show that the
method reproduces the STS results or a Treanor distribution depending on the
choice of the boundary conditions. A positive drift, whose energy onset is
determined by the vibrational to translational temperature ratio, brings
molecules from mid-energy range to dissociation. The high-energy fall of the
distribution is observed even neglecting VT processes which are normally
believed to be its cause. Our study explains several puzzling features of
previous studies, provides new insights into the control of the dissociation
rate and a much sought compression of the required data for modeling.
