Herschel Space Observatory - Theoretical Research Proposal #1022

Computation of High-Resolution Spectra of Methanol and Methyl Cyanide

Principal Investigator: Timothy Lee    
           Institution: NASA Ames Research Center

Co-Investigators:
David Schwenke, NASA Ames Research Center
Xinchuan Huang, NASA Ames Research Center (NPP)

Dollars Approved: 198504

Abstract:
Molecules with large amplitude motions possess complexity in their ro-vibrational
and purely rotational spectra. Because of this complexity, they are ideal molecules
to be used to characterize the physical conditions of the galactic objects in which
they are observed, which was noted more than two decades ago by Ho and Townes. 
However, for the Herschel HiFi instrument such molecules have been dubbed “weeds”
because they will add considerable spectral congestion.  One of the biggest
challenges to be overcome in analyzing data from HiFi is the identification and
possibly elimination (through subtraction) of spectral lines due to weed molecules. 
Two molecules that were identified at a Herschel Laboratory Workshop in late 2006 as
important “weeds” are methanol (Class 1) and methyl cyanide (Class 2).  It has been
demonstrated over the last decade that the state-of-the art in producing accurate
line lists for molecules, especially those with a large amplitude motion, consists
of a combination of ab initio theory with high-resolution laboratory data.  We
propose to apply this procedure, described in detail in the proposal, to the
methanol and methyl cyanide molecules.  The output from this research will be highly
accurate and complete line lists, including intensities, for methanol and methyl
cyanide that will be made readily available to the Herschel science community for
use in analyzing their HiFi data.