THE FORMATION AND ROLE OF WATER DIMERS IN A COMETARY ATMOSPHERE, WITH APPLICATION TO COMET-P HALLEY

The formation of water dimers in a cometary coma is comprehensively modeled, using recent thermochemical data and plausible chemical schemes. For P/Halley at the time of the 1986 flyby missions, the computed dimer mole fraction is everywhere smaller than 10(-5). The model is also used to confirm the earlier results of Crifo concerning the partial recondensation of the coma water into large clusters, which unavoidably follows the formation of the dimers.