Solar fluorescence model of CH3D as applied to comet emission
Abstract
We developed a solar fluorescence emission model for the ν4 band of CH3D for application to low-density, optically thin environments like cometary atmospheres. Our model utilizes transition frequencies, energy levels, and line strengths from the HITRAN 2008 database. We calculated the statistical weights of states with A-type and E-type spin symmetry, the partition functions for each spin manifold as a function of rotational temperature, and the Einstein A- and B-coefficients for individual rotational-vibrational transitions. We used these parameters to construct a database of fluorescence efficiencies (g-factors) at rotational temperatures relevant to cometary atmospheres. The effects of nuclear spin temperature and rotational temperature on the resulting g-factors are disentangled and modeled separately. The primary application of this model is to constrain the abundance ratio CH3D/CH4 in cometary ice, a possible cosmogonic parameter. We present the upper limit for CH3D/CH4 in comet C/2007 N3 (Lulin) using our model and illustrate the ability of current spectrometers to stringently constrain astrochemical model predictions for CH3D/CH4 in the early solar system.
- Publication:
-
Journal of Molecular Spectroscopy
- Pub Date:
- September 2013
- DOI:
- 10.1016/j.jms.2013.05.007
- Bibcode:
- 2013JMoSp.291..118G