The Photodissociation of Formaldehyde in Comets
Abstract
Observations of comets in the 905-1180 Å spectral band made with the Far Ultraviolet Spectroscopic Explorer in 2001 and 2004 show unusual features in the fluorescent emissions of CO and H2. These include emission from a non-thermal high-J rotational population of CO and solar Lyα induced fluorescence from excited vibrational levels of H2, both of which are attributed to the photodissociation of formaldehyde. In this paper we model the large number of observed H2 lines and demonstrate the dependence of the pumping on the heliocentric velocity of the comet and the solar line profiles. We also derive the rotational and vibrational populations of H2 and show that they are consistent with the results of laboratory studies of the photodissociation of H2CO. In addition to the principal series of H i and O i, the residual spectrum is found to consist mainly of the Rydberg series of C i multiplets from which we derive the mean carbon column abundance in the coma. Fluorescent emissions from N i and N2 are also searched for.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2015
- DOI:
- 10.1088/0004-637X/812/2/115
- Bibcode:
- 2015ApJ...812..115F
- Keywords:
-
- comets: individual: C&2001 A2;
- C&2001 Q4;
- ultraviolet: planetary systems