Spitzer Space Telescope - Theoretical Research Proposal #20275


Unfolding the Information of the Interstellar H$_2$ Spectrum:  Its
impact on Spitzer IR Observations

Principal Investigator: Gary Ferland
           Institution: University of Kentucky

Co-Investigators: 
Teck Ghee Lee, University of Kentucky and Oak Ridge National Lab      
David R. Schultz, Oak Ridge National Lab                              
Phillip C. Stancil, University of Georgia                             

Science Category: ISM 
Dollars Approved: 51444.0 

Abstract:
Molecular hydrogen is the most ubiquitous molecule in the universe.
H$_2$ plays a pivotal role in a variety of processes that
significantly influence the chemical and physical state of
interstellar gas.  However, the lack of both accurate and complete
collisional data sets for rovibrational inelastic cross sections and
rate coefficients for H, He, and H$_2$ impacting the dominant
molecular species (e.g.  H$_2$, HD, and CO) has created a serious set
back in the development of reliable astrophysical models complementing
NASA's {it Spitzer} IR observations.  It has been shown that the
uncertainties in the existing collisional rate coefficient data can be
significant.  Modeling and interpretation of observations of such
environments require quantitatively accurate and complete treatment of
H$_2$.  To derive significant scientific return from the unprecedented
observations that are expected in the near future, we propose to
compute rovibrational excitation and dissociation cross sections and
rate coefficients for collisions of H, H$_2$ and He with H$_2$ and HD
for all transitions between all bound rovibrational levels of the
target molecules using continued development of well established
quantum mechanical close-coupling and classical trajectory methods.
Rate coefficients will be computed from 10  to 50,000~K and fit to
convenient functional forms with physical low- and high-temperature
limits.  The results of this proposal will then enable models, such as
the very widely used and tested spectral modeling code Cloudy, to
reliably simulate these astrophysical environments, leading to deeper
examination and understanding of their physical properties through {it
Spitzer} observations of H$_2$ features.