Spitzer Space Telescope - Archive Research Proposal #30144


Diamonds are a PAHs Best Friend

Principal Investigator: Louis Allamandola
           Institution: NASA Ames Research Center

Co-Investigators: 
Andrew Mattioda, SETI                                                 
Els Peeters, SETI                                                     
Douglas Hudgins, NASA Ames Research Center                            
Alexander Tielens, NASA Ames Research Center                          
Charles Bauschlicher, Jr., NASA Ames Research Center                  

Science Category: ISM 
Dollars Approved: 56727.0 

Abstract:
The mid-IR spectroscopic capabilities and unprecedented sensitivity of
the Spitzer Space Telescope has shown that the ubiquitious infrared
(IR) emission features can be used as probes of many galactic and
extragalactic objects.  These features, formerly called the
Unidentified Infrared (UIR) Bands, are now generally attributed to the
vibrational emission from polycyclic aromatic hydrocarbons, PAHs, and
related species.  However there is some difficulty in reproducing all
the features of the interstellar emission spectrum solely with PAH
spectra.  Because these differences have persisted as our knowledge of
PAH spectroscopy has increased these differences point to at least one
other type of contributor to the interstellar emission spectrum.  The
association of these features with objects abundant in cosmic carbon
points to an additional carbonaceous material contributing to the
features.  Among the possibilities diamonds are particularly
attractive.  However, until very recently, this could not be tested
because well-characterized microdiamonds were not available for study.
These are now available for purchase from ChevronTexaco.  We propose
to use the matrix isolation technique to measure the 0.7 to 20  µm
spectra of astrophysically relevant, cold microdiamonds.  We will also
develop and apply the computational techniques required to calculate
these spectra and the spectra of microdiamonds for which we cannot
obtain samples.  Given the lack of availability of microdiamonds until
recently, their IR spectroscopic properties are not known.  Since
microdiamonds have been long thought to be present throughout the ISM
this lack of spectroscopic information prevents a complete analysis of
Spitzer data, especially in the 7 to 8 µm region.  These data will be
made available to the astronomical community.  Incorporating these new
data into existing models will improve their ability to probe
conditions such as radiation field, charge state, electron and
hydrogen density, and cosmochemical history of the object.