  The kinetics and energetic relaxation associated with collisions between fast
and thermal atoms are of fundamental interest for escape and therefore also for
the evolution of the Mars atmosphere. The total and differential cross-sections
of fast O($^3P$) atom collisions with CO have been calculated from quantum
mechanical calculations. The cross-sections are computed at collision energies
from 0.4 to 5 eV in the center-of-mass frame relevant to the planetary science
and astrophysics. All the three potential energy surfaces ($^3$A', $^3$A" and 2
$^3$A" symmetry) of O($^3P$) + CO collisions separating to the atomic ground
state have been included in calculations of cross-sections. The cross-sections
are computed for all three isotopes of energetic O($^3P$) atoms collisions with
CO. The isotope dependence of the cross-sections are compared. Our newly
calculated data on the energy relaxation of O atoms and their isotopes with CO
molecules will be very useful to improve the modeling of escape and energy
transfer processes in the Mars' upper atmosphere.
