Chemistry of O(1D) atoms in the coma:: Implications for cometary missions

The forbidden red oxygen lines at 6300 and 6364 Angstrom, which results due to D-1-->P-3 transition, provide an important diagnostic tool in the study of comets. These lines cannot be produced by resonance fluorescence excitation of the ground-state oxygen atom, and therefore are mainly produced due to dissociation of H2O and other O-containing species in comets (e.g., OH, CO, CO2, H2CO etc.) by photon and electron impact and in other collision reactions. Since the lifetime of 1 D state is quite long (similar to110 see) collisional de-excitation processes are important. We have used a coupled chemistry-transport model in conjunction with an efficient emission production code to study the chemistry of 0(D-1) atoms and the production of OI 6300 Angstrom emission in comets. The model calculations are made for comet 46P/Wirtanen: the target of the ROSETTA mission. It is found that in the inner coma the density profile of O(D-1) is controlled dominantly by the H2O. The model predicts similar to300 R of OI 6300 Angstrom brightness on comet Wirtanen. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.