Astronomy and Astrophysics – Astronomy
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007sptz.prop40645l&link_type=abstract
Spitzer Proposal ID #40645
Astronomy and Astrophysics
Astronomy
Scientific paper
Molecules with large amplitude motions possess significant complexity in their rovibrational and purely rotational spectra. Because of this complexity, they are ideal molecules to be used to characterize the physical conditions of the celestial objects and galactic environments in which they are observed, which was noted more than two decades ago by Ho and Townes. The simplest and best characterized molecule with a large amplitude motion of interest in astronomy is ammonia. The available experimental data for even this molecule, however, is not sufficient to generate a synthetic spectrum that compares well with observations from the Spitzer Space Telescope of one of the coolest known T dwarfs Gl570D, and this is likely to be the case for any celestial environments above 400K. The IRS instrument on the Spitzer Space Telescope has already recorded spectra that cannot be well modeled and interpreted using the available experimental data for ammonia. In response to the urgent need for better line lists, including intensities, we propose to use the tools of theoretical spectroscopy, combined with refinement using the available experimental data, to obtain highly accurate line lists for ammonia and its isotopomers. Through the use of high accuracy electronic structure calculations, and refinement of the resulting potential energy surface (PES) with the available experimental data, Schwenke has already constructed highly accurate lists for all isotopomers of the water molecule. The accuracy of the resulting PES, transition energies, and intensities has been demonstrated by later spectroscopic studies. We propose to use a similar approach for ammonia. Our approach will be to use high-level electronic structure calculations to construct a highly accurate, isotope independent PES and dipole surface for the ammonia molecule. The resulting highly accurate PESs and dipole moment surfaces will then be used to solve the nuclear Schroedinger equation to generate the necessary line lists.
Huang Xinchuan
Lee Timothy
Schwenke David
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