Unidentified bands in comet Ikeya-Zhang (C/2002 C1):: The correlation between unidentified bands and H2O+

We report the results of the low-dispersion spectroscopic observations of comet Ikeya-Zhang (C/2002 C1) performed from 2002 March 10 to 20. The unidentified molecular bands that have been recognized in the plasma tail of several comets are detected in an antisunward coma of the comet Ikeya-Zhang. Our observations show the flux of unidentified bands at 5310 Angstrom is correlated to the flux of H2O+ as reported for three comets by S. Wyckoff et al. The observed column density ratio between H2O+ and CO+, and the flux ratio between the unidentified bands and CO+ varied day by day, by a factor of approximate to2 in our observations. However, it appears that the ratios are proportional to each other. We conclude that a parent of unidentified bands is produced from or generates H2O+ directly or indirectly. We propose the hypothesis that H2O+ is the parent of the unidentified bands since similar structures of emission bands are recognized in some laboratory studies on charge transfer collisions between neutral water and Ar+ or N-2(+).