tokens: being only due to reflection by dust in the coma. The fitted one-dimensional dust spectrum was used to determine the scaling factor for the dust profile by measuring the relative strength of the continuum in the centre of the emission band compared to that in the centre of the dust region. The scaled dust profile was subtracted from the emission profile to leave the contribution due to the gas only. The measured spatial fluxes were converted to column densities using the fluorescence efficiencies for each species. The fluorescence efficiencies for the OH (0-0), NH (0-0) and CN (0-0) features are strongly dependent on the heliocentric velocity of the comet due to the Swings effect (Swings 1941 ), and were determined using D. Schleicher’s online tool 2 . The C 3 (λ4050) and the C 2 (Δ = 0) fluorescence efficiencies were taken from AH95 and C12 , while the NH 2 (0,3,0) fluorescence efficiency was that used by Fink ( 2009 ). The fluorescence efficiencies were scaled as . The Haser model (Haser 1957 ) describes the photodissociation of parent molecules into daughter molecules in a spherically symmetric coma. The column density of the daughter molecules N d as a function of distance from the nucleus ρ for a molecular production rate Q is given by the equation where K 0 ( y ) is a modified Bessel function of the second kind. The quantities l p and l d are the scalelengths of the parent and daughter molecules, respectively, and is the radial outflow velocity which is calculated using the equation from Cochran Schleicher ( 1993 ): A model Haser profile was fit to the measured column density profile of each observed species to determine its production rate. The nucleus was placed at the centre of the slit for each exposure, and therefore the extracted profiles have components at ρ values either side of the nucleus. As the Haser model assumes spherical symmetry in the coma, the profiles in the two directions were averaged and the production rates were determined using these average profiles. A series of model profiles for different values of the production rate were generated, and the model profile where the χ 2 statistic was minimized gave the best-fitting production rate. The additional uncertainty in Q was determined by finding the difference between the best-fitting production rate and the model production rate where (Hughes Hase 2010 ). We measured the molecular production rates using scalelengths from two sources, which are given in Table 4 . The production rates in Table 5 were determined using the scalelengths from AH95 , while those in Table 6 used the scalelengths from C12 . We chose to use the same set of fixed scalelengths as previous authors to allow direct comparison of our abundance ratio measurements with the ratios determined in those studies. The parent and daughter scalelengths are usually scaled as , but Langland-Shula Smith ( 2011 ) note that the theoretical scalelength variation should instead be . Power-law fitting can be carried
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