The interaction of the thermosphere and ionosphere is largely governed
by collisions between ions and neutral particles. On Venus and the Ea
rth, O+ is a dominant ion, and atomic O dominates throughout much of t
he thermosphere; therefore an accurate O+-O cross section is an import
ant prerequisite for understanding the dynamics of planetary upper atm
ospheres. The cross section and momentum transfer collision frequency
are calculated with a quantum mechanical code which includes resonance
charge exchange, polarization, and charge-quadrupole effects. Our res
ults agree well with earlier calculations of Stubbe [1968] and Stallco
et al. [1991].