Search for S_2_ and Naphtalene in Comets Halley Honda-Mrkos-Pajdusakova and Hyakutake 1996 B2

The main features of cometary spectra in the 250-350 nm range are: the CS(0,0) and (0,1) bands; OH(1,0), (0,0),and (1,1) bands; CO2+ bands at 289 nm and 326 nm and teh NH(0,0) band at 336 nm. The spectra of Comet Halley obtained at short distances from the nucleus by the Vega three-channel spectrometer show an additional emission at 323 nm. A good candidate for this band is naphthalene emitting fluorescence radiation in the S1-S0 transition. Observations of Comet Honda-Mrkos-Pajdusakova in the same wavelength range were obtained with IUE between February 10 and 15. Part of the Honda IUE observation program was transfered to comet Hyakutake 1996 B2. In the spectra, the feature at 323 nm is not present, given the sensitivity level of IUE at this wavelength. We have made a comparison of the synthetic spectrum of S2 with the cometary spectra. Coincidences between measured and predicted features may be observed at 286.1, 292.2, 295.6, 302.0, 317.2, 320.3 and 321.2 nm. It may be concluded that the IUE spectra of Hyakutake indicate the possible presence of S2 in the spectral region 280-325 nm.