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Title: POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION

Abstract

Polycyclic aromatic hydrocarbons (or PAHs) have been the subject of astrochemical research for several decades as principal sources of the interstellar aromatic infrared emission bands. PAH clusters could possibly contribute to these emission bands, but a lack of data on their infrared properties has made this hypothesis difficult to evaluate. Here we investigate homogeneous neutral PAH clusters by measuring the mid-infrared absorption spectra of the five nonlinear PAH molecules phenanthrene, chrysene, pyrene, perylene, and benzo[ghi]perylene within solid argon ice at a fixed temperature of 5 K. We attribute observed spectral shifts in their principal absorption bands as a function of argon/PAH ratio to clustering of the PAH molecules within the argon matrix. These shifts are related to the cluster structures forming in the matrix and the topology of the monomer PAH molecule. We predict that interstellar PAH molecules that are relatively large (no fewer than 50 carbon atoms per molecule) and compact will have clusters that contribute to the asymmetrically red-shaded profile of the interstellar 11.2 μm emission band.

Authors:
;  [1]
  1. NASA Ames Research Center, Mail Stop 245-6, Building N245, Room 148, P.O. Box 1, Moffett Field, CA 94035 (United States)
Publication Date:
OSTI Identifier:
22521383
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 801; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; ABSORPTION SPECTRA; ARGON; ATOMS; CHRYSENE; EMISSION SPECTRA; ICE; INTERMEDIATE INFRARED RADIATION; INTERSTELLAR SPACE; MOLECULES; MONOMERS; NONLINEAR PROBLEMS; PERYLENE; PHENANTHRENE; POLYCYCLIC AROMATIC HYDROCARBONS; PYRENE; SPECTRAL SHIFT

Citation Formats

Roser, J. E., and Ricca, A., E-mail: Joseph.E.Roser@nasa.gov. POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION. United States: N. p., 2015. Web. doi:10.1088/0004-637X/801/2/108.
Roser, J. E., & Ricca, A., E-mail: Joseph.E.Roser@nasa.gov. POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION. United States. doi:10.1088/0004-637X/801/2/108.
Roser, J. E., and Ricca, A., E-mail: Joseph.E.Roser@nasa.gov. Tue . "POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION". United States. doi:10.1088/0004-637X/801/2/108.
@article{osti_22521383,
title = {POLYCYCLIC AROMATIC HYDROCARBON CLUSTERS AS SOURCES OF INTERSTELLAR INFRARED EMISSION},
author = {Roser, J. E. and Ricca, A., E-mail: Joseph.E.Roser@nasa.gov},
abstractNote = {Polycyclic aromatic hydrocarbons (or PAHs) have been the subject of astrochemical research for several decades as principal sources of the interstellar aromatic infrared emission bands. PAH clusters could possibly contribute to these emission bands, but a lack of data on their infrared properties has made this hypothesis difficult to evaluate. Here we investigate homogeneous neutral PAH clusters by measuring the mid-infrared absorption spectra of the five nonlinear PAH molecules phenanthrene, chrysene, pyrene, perylene, and benzo[ghi]perylene within solid argon ice at a fixed temperature of 5 K. We attribute observed spectral shifts in their principal absorption bands as a function of argon/PAH ratio to clustering of the PAH molecules within the argon matrix. These shifts are related to the cluster structures forming in the matrix and the topology of the monomer PAH molecule. We predict that interstellar PAH molecules that are relatively large (no fewer than 50 carbon atoms per molecule) and compact will have clusters that contribute to the asymmetrically red-shaded profile of the interstellar 11.2 μm emission band.},
doi = {10.1088/0004-637X/801/2/108},
journal = {Astrophysical Journal},
number = 2,
volume = 801,
place = {United States},
year = {Tue Mar 10 00:00:00 EDT 2015},
month = {Tue Mar 10 00:00:00 EDT 2015}
}