Oxygen/hydrogen chemistry in the inner comae of active comets

We have constructed a concentric-shell, one-dimensional kinetic model that examines the chemistry of hydrogen and oxygen species in detail. We have studied the effects of the reactions of the reactive OH, O(³P), and O( ¹D) species with themselves and with the abundant stable molecules in the inner coma of moderately and highly active comets. We find that the reactions (1) O(¹D) + H₂O → 2OH and (2) O( ³P) + OH → O₂ + H play important roles in the inner comae of active comets. Inclusion of reaction (2) predicts the formation of significant amounts of molecular oxygen. As the densities of O₂ may be as high as 1% those of water in some cases, the possibility of detection exists. We suggest the possibility that the ion O₂⁺ may contribute to some previously unassigned features in the optical ion-tail spectra of comets. We also consider the role that reactions of the reactive species might play in the destruction of CO, NH₃, and organic molecules in the inner coma of the active comet. We find that destruction of formaldehyde, for example, by reaction with OH has a small but essentially negligible effect on the predicted production rate of formaldehyde. Finally, we examine the significance of the reaction of OH with CO in the dense inner coma.