Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011mwac.meet..p03s&link_type=abstract
Midwest Astrochemistry Meeting 2011, held 21-22 October at the University of Illinois at Urbana-Champaign. http://midwest.astroc
Astronomy and Astrophysics
Astronomy
Scientific paper
Large, symmetric molecules, such as linear carbon chains, polycyclic aromatic hydrocarbons (PAHs), and fullerenes are important to interstellar chemistry, but cannot be observed by rotational spectroscopy because they lack a permanent dipole moment. In particular, buckminsterfullerene (C60) has recently been detected by infrared emission spectroscopy in many environments. To better understand the interstellar chemistry of C60, it will be necessary to observe it in environments which are not favorable for emission. To aid in astronomical searches for C60 absorption signals, we are working on obtaining a cold, gas-phase spectrum of C60. To do so, we are using a hot oven for generating gas-phase sample and then cooling the molecules using a supersonic expansion. It is unknown whether this technique will be sufficient to cool a molecule as large as C60 to the point where it can observed by absorption spectroscopy.
As an intermediate step, we have acquired a rotationally-resolved infrared spectrum of the PAH pyrene (C16H10) to test cooling of large molecules by supersonic expansion. Our spectra were obtained using an infrared cavity ringdown spectrometer based on a quantum cascade laser near 8.5 μm. Though it is small compared to C60, pyrene is the largest molecule to be observed with rotational resolution by absorption spectroscopy. We have fit the spectrum to an effective asymmetric top Hamiltonian and have found that this molecule behaves like an almost ideal rigid rotor. We have also found that the pyrene molecules are cooled to a rotational temperature of ~25 K and estimate that the vibrational temperature is 25 - 90 K.
Brumfield Brian E.
McCall Benjamin J.
Stewart Jacob T.
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