The 3.4 micrometer emission feature in Comet Halley

Several teams of ground based observers reported observations of the emission feature centered at 3.36 micrometers in comet Halley following its discovery by the Vega 1 spacecraft. The position and shape of the band indicate a superposition of emissions by C-H groups. But the mechanism for the excitation of these C-H3 groups is still not agreed upon. Three possibilities are summarized. Elucidation of the emission mechanism is needed to determine whether the source is predominately solid or gas. In addition, is it shown that the derived carbon abundance in Halley depends strongly on the assumed mechanism.