OBSERVATIONS AND ANALYSIS OF O(D-1) AND NH2 LINE-PROFILES FOR THE COMA OF COMET P/HALLEY

A set of high-resolution Fabry-Perot measurements of the coma of comet P/Halley was acquired in the [O I] 6300 Angstrom and NH2 6298.62 Angstrom emission lines. These high-resolution measurements provide the first optical observations capable of studying directly the photochemical kinetics and dynamic outflow of the coma. The observations were analyzed by a Monte Carlo Particle Trajectory Model. The agreement of the model and observed line profiles was excellent and verified the underlying dynamics, exothermic photodissociative chemistry, and collisional thermalization in the coma. The somewhat wider intrinsic line profile width for the O(D-1) emission in 1986 January compared to 1986 May is, for example, produced by the larger outflow speeds and gas temperatures nearer perihelion in January. The January O(D-1) profile, which is wider than the January NH2 profile, is indicative of the photochemical kinetics in the dissociation of the parent molecules H2O and OH in the coma. The absolute calibration of the observations in 1986 January allowed the production rates for H2O and the NH2-parent molecules to be determined. The average daily water production rates derived from the O(D-1) emission data for January 16 and 17 are (2.90+/-0.13) x 10(30) molecules s(-1) and (2.68 +/- 0.38) x 10(30) molecules s(-1), respectively. These very large water production rates are consistent with the extrapolated (and 7.6 day time variable) water production rates determined from the analysis of lower spectral resolution observations for O(D-1) and Ha emissions (Smyth et al. 1993) that covered the time period up to January 13. The large production rates on January 16 and 17 establish that the maximum water production rate for comet Halley occurred pre-perihelion in January. Implications drawn from comparison with 18 cm radio emission data in January suggest that the peak water production rate was even larger and might have been as large as similar to 3.6 x 10(30) molecules s(-1) near January 23. The average production rate for NH, determined from the NH2 emission data for January 17 was (1.48 +/- 0.10) x 10(28) molecules s(-1), yielding an NH3/H2O production rate ratio of 0.55%. This ratio is consistent with the range of earlier derived values. The corrected g-value noted in the NH2 analysis brings most NH2 production rates in line with NH production rates and also makes them consistent with the production of both species from NH3.