The vibrational distribution of the O2 + product ion in the reaction of O+ with CO2 has been measured in a selected ion flow tube using the monitor ion technique. At 300 K the measured vibrational distribution is 45% of the ions in v=1, 32% in v≥2 and 23% in v=0. However, it is possible that vibrational quenching by the monitor gas may affect the distribution, and the nascent population may be entirely in v>0. The branching ratio between the O2 ++CO and the CO2 ++O product channels has also been measured as a function of ion drift velocity. The implications of these experiments for terrestrial releases of CO2 into the ionosphere and for the ionospheres of Mars and Venus are considered. ¿ American Geophysical Union 1991