Abstract
The ortho-to-para ratio (OPR) of a cometary molecule is one of primordial character in comets. The OPR which is characterized by a spin temperature, is thought to reflect the formation conditions of the molecule. In this paper we show the high-dispersion spectrum of cometary NH2 in Comet C/2001 A2 (LINEAR), from which the OPR of NH2 is determined based on the fluorescence excitation model. Since the NH2 is a photodissociation product of cometary ammonia, we applied the permutation group theory to the whole reaction system (i.e. the photodissociation reaction of ammonia to NH2 and H) in order to derive the OPR of ammonia from that of NH2.
The derived OPR of ammonia is 1.12 ± 0.03 in Comet C/2001 A2 (LINEAR). This value corresponds to a spin temperature of 30 +3−2 K. If this reflects the temperature where the comet formed in the protosolar nebula, our result indicates that this comet was formed in the region of the giant planets between Jupiter and Neptune.
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Kawakita, H., Watanabe, JI., Fuse, T., Furusho, R., Abe, S. (2002). Spin Temperature of Ammonia Determined from NH2 in Comet C/2001 A2 (LINEAR). In: Boehnhardt, H., Combi, M., Kidger, M.R., Schulz, R. (eds) Cometary Science after Hale-Bopp. Springer, Dordrecht. https://doi.org/10.1007/978-94-017-1088-6_37
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DOI: https://doi.org/10.1007/978-94-017-1088-6_37
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