Herschel Space Observatory - Theoretical Research Proposal #1017

Spectroscopy of Deuterated Molecular Ions

Principal Investigator: Takeshi Oka    
           Institution: University of Chicago

Dollars Approved: 181728

Abstract:
One of the most surprising developments in molecular astrophysics in the last
several years has been the observation of enormously high deuterium fractionation in
the low temperature and high density region of pre-stellar cores. The ND3/NH3 ratio
of ~ 10-3 observed in the Barnard 1 Cloud corresponds to fractionation by a factor
of ~1012. This extraordinary phenomenon has been explained as due to deuterium
fractionation of H3+ to H2D+, HD2+ and D3+, and their subsequent deuteron donation
to molecules.  Implicit in the calculations is analogous deuterium fractionation of
other simple fundamental molecular ions, for example, the fractionation of CH3+ to
CH2D+, CHD2+, and CD3+. The exothermicities of the latter reaction chain are twice
as high as those for the H3+ chain reactions and should proceed efficiently even at
higher temperatures than the H3+ analogue.  
We propose to systematically conduct laboratory mid- and near- infrared spectroscopy
of deuterated species of fundamental molecular ions containing one heavy atom such
as CHD+, CD2+, CH2D+, CHD2+, NHD+, NH2D+, NHD2+, NHD3+, NH2D2+, NHD3+, HDO+, H2DO+,
HD2O+ to determine their rotational constants so that users of the Herschel Space
Observatory can search for their spectra using the Hetrodyne Instrument for the
Far-Infrared.  The breakdown of molecular symmetry due to deuteration opens up rich
spectra in the wavelength range of HIFI for further studies of pre-stellar cores and
other low temperature high density regions which may have the key to star formation.
 The hydrogenic molecular ions have already been studied in our laboratory and the
extension to deuterated species should be straightforward albeit time consuming.