Herschel Space Observatory - Theoretical Research Proposal #1029

IR Spectroscopy of Polycyclic Aromatic Hydrocarbons

Principal Investigator: Andrew Mattioda
           Institution: NASA Ames Research Center

Co-Investigators:
Louis Allamandola, NASA Ames Research Center
Charles Bauschlicher Jr, NASA Ames Research Center


Dollars Approved: 196984

Abstract:
Herschel, scheduled to launch in 2008, will make pioneering spectroscopic
observations across the Far-IR.  The mid-IR spectra of many objects Herschel will
study are dominated by the emission bands attributed to polycyclic aromatic
hydrocarbons (PAHs). Since PAHs also have bands that span the Far-IR, PAHs will
contribute to the Herschel spectra of the sources that show the mid-IR PAH features.
Proper interpretation of these spectra requires the availability of the Far-IR
spectra of PAHs measured under conditions relevant to astrophysics.  These are not
available.  This is a proposal to start providing that data.   
We propose to
experimentally measure and theoretically compute the spectroscopic properties of
cold, isolated PAHs in the 20-200 µm wavelength range. We plan to study 20 PAHs. 
Two PAHs in our sample have structures that incorporate 5-membered rings and six
PAHs incorporate nitrogen atoms. The remaining twelve PAHs contain between 30 and 50
 carbon atoms and sample different geometries, edge structures, and symmetries.
These FIR spectra, along with our mid-IR spectra, will be made available to the
community through a database and open website that is now in development. This work
will also be described in the peer-reviewed literature.
PAH bands longward of 20 µm
give information fundamentally different from that of the mid-IR features. Thus,
Herschel's spectroscopic observations have the potential to make significant,
fundamental contributions to the astrochemistry and astrophysics of the emission
zones.