Large-aperture [O I] 6300 Å photometry of comet Hale-Bopp:: Implications for the photochemistry of OH

Large-aperture photometric observations of comet Hale-Bopp (C/1995 O1) in the forbidden red line of neutral oxygen ([O I] 6300 Angstrom) with the 150 mm dual-etalon Fabry-Perot spectrometer that comprises the Wisconsin H alpha Mapper and a 50 mm dual-etalon Fabry-Perot spectrometer at the McMath-Pierce main telescope from 1997 late February to mid April yield a total metastable O(D-1) production rate of (2.3- 5.9) x 10(30) s(-1). Applying the standard H2O and OH photodissociation branching ratios found in Huebner, Keady, & Lyon and van Dishoeck & Dalgarno, we derive a water production rate, of Q(H2O), of (2.6-6.1) x 10(31) s(-1), which disagrees with Q(H2O) approximate to 1 x 10(31) s(-1) determined by independent H2O OH, and H measurements. Furthermore, our own [O I] 6300 Angstrom observations of the inner coma (< 30,000 km) using the 3.5 m Wisconsin-Indiana-Yale-NOAO telescope Hydra and Densepak multi-object spectrographs yield Q(H2O) 1 x 10(31) s(-1). Using our [O I] 6300 <Angstrom> data, which cover spatial scales ranging from 2,000 to 1 x 10(6) km, and a complementary set of wide-field ground-based OH images, we can constrain the sources of the apparent excess O(D-1) emission to the outer coma, where photodissociation of OH is assumed to be the dominant O(D-1) production mechanism. From production rates of other oxygen-bearing volatiles (e.g., CO and CO2), we can account for at most 30% of the observed excess O(D-1) emission. Since even less O(D-1) should be coming from other sources (e.g., electron excitation of neutral O and distributed nonnuclear sources of we hypothesize that the bulk of the excess O(D-1) is likely coming from photodissociating OH. Using the experimental OH photodissociation cross section of Nee & Lee at Ly alpha as a guide in modifying the theoretical OH cross sections of van Dishoeck & Dalgarno, we can account for approximate to 60% of the observed O(D-1) excess without requiring major modifications to the other OH branching ratios or the total OH photodissociation lifetime.