We have constructed a synthetic spectrum of the 2.5 micron C2H C2H bands and compared them with diminutive structures in the near-infrared spectra of Comets P/Halley and West (1976 VI). We found that the Q branches of the C2H C2H bands coincide with two small emission peaks in the spectra of the comets. We undertook Monte Carlo simulations using observed emission intensities of C2 C2 and possibly C2H C2H in Comet P/Halley in order to derive a lifetime range of C2H C2H and a production rate at the time of observations of P/Halley. We obtained a C2H C2H production rate of 1×1027sec−1 1×1027sec−1 for P/Halley on December 20, 1985, assuming the 2.5 micron features are due to C2H C2H . We derived a very short lifetime (<100 seconds) of C2H C2H at 1AU heliocentric distance, assuming that the only parent molecule for C2H C2H and C2 C2 is C2H C2H . Using this short lifetime we were unable to fit our C2 C2 distribution model to C2 C2 distribution curves observed by O'Dell et al.(1988), because our curve shows a steep slope compared with the observed one. We conclude that there must be significant additional source(s) for C2H C2H and C2 C2 other than C2H2 C2H2 .

• KIM SANG JOON(Department of Astronomy and Space Science, Kyunghee University)