Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published April 1, 2014 | Published + Submitted
Journal Article Open

Laboratory Determination of the Infrared Band Strengths of Pyrene Frozen in Water Ice: Implications for the Composition of Interstellar Ices


Broad infrared emission features (e.g., at 3.3, 6.2, 7.7, 8.6, and 11.3 μm) from the gas phase interstellar medium have long been attributed to polycyclic aromatic hydrocarbons (PAHs). A significant portion (10%-20%) of the Milky Way's carbon reservoir is locked in PAH molecules, which makes their characterization integral to our understanding of astrochemistry. In molecular clouds and the dense envelopes and disks of young stellar objects (YSOs), PAHs are expected to be frozen in the icy mantles of dust grains where they should reveal themselves through infrared absorption. To facilitate the search for frozen interstellar PAHs, laboratory experiments were conducted to determine the positions and strengths of the bands of pyrene mixed with H_2O and D_2O ices. The D_2O mixtures are used to measure pyrene bands that are masked by the strong bands of H_2O, leading to the first laboratory determination of the band strength for the CH stretching mode of pyrene in water ice near 3.25 μm. Our infrared band strengths were normalized to experimentally determined ultraviolet band strengths, and we find that they are generally ~50% larger than those reported by Bouwman et al. based on theoretical strengths. These improved band strengths were used to reexamine YSO spectra published by Boogert et al. to estimate the contribution of frozen PAHs to absorption in the 5-8 μm spectral region, taking into account the strength of the 3.25 μm CH stretching mode. It is found that frozen neutral PAHs contain 5%-9% of the cosmic carbon budget and account for 2%-9% of the unidentified absorption in the 5-8 μm region.

Additional Information

© 2014 American Astronomical Society. Received 2014 January 1; accepted 2014 February 14; published 2014 March 18. This research was carried out at the Jet Propulsion Laboratory and IPAC, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Support for this research was provided in part by funding from the NASA Astrobiology Institute to Rensselaer Polytechnic Institute (award NNA09DA80A). The experimental part of this work was enabled through partial funding from the Jet Propulsion Laboratory's DRDF and R&TD funding for infrastructure of the "Ice Spectroscopy Laboratory" and was carried out by H.L. and M.S.G., supported by an astrophysics laboratory research award funded by the Spitzer Space Telescope. H.L. also acknowledges the Finnish Cultural Foundation for financial support. We thank Dr. Irene Li Barnett and Dr. Antti Lignell, who were involved in building the experimental setup used and initial training of H.L. Data analysis was carried out by E.H–U. at the California Institute of Technology (supervised by A.B. and M.S.G.), funded by an IPAC Visiting Graduate Student Fellowship.

Attached Files

Published - 0004-637X_784_2_172.pdf

Submitted - 1403.4663v1.pdf


Files (5.5 MB)
Name Size Download all
2.8 MB Preview Download
2.6 MB Preview Download

Additional details

August 22, 2023
October 26, 2023