The CO2 production rate has been derived in comets using the Cameron band
(a3Pi - X1Sigma) emission of CO molecule assuming that photodissociative
excitation of CO2 is the main production mechanism of CO in a3Pi metastable
state. We have devoloped a model for the production and loss of CO(a3Pi) which
has been applied to comet 103P/Hartley 2: the target of EPOXI mission. Our
model calculations show that photoelectron impact excitation of CO and
dissociative excitation of CO2 can together contribute about 60-90% to the
Cameron band emission. The modeled brightness of (0-0) Cameron band emission on
comet Hartley 2 is consistent with Hubble Space Telescope observations for 3-5%
CO2 (depending on model input solar flux) and 0.5% CO relative to water, where
photoelectron impact contribution is about 50-75%. We suggest that estimation
of CO2 abundances on comets using Cameron band emission may be reconsidered. We
predict the height integrated column brightness of Cameron band of ~1300 R
during EPOXI mission encounter period.Comment: 3 figure
