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Single photon infrared emission spectroscopy: a study of IR emission from UV laser excited PAHs between 3 and 15 micrometersSingle-photon infrared emission spectroscopy (SPIRES) has been used to measure emission spectra from polycyclic aromatic hydrocarbons (PAHs). A supersonic free-jet expansion has been used to provide emission spectra of rotationally cold and vibrationally excited naphthalene and benzene. Under these conditions, the observed width of the 3.3-micrometers (C-H stretch) band resembles the bandwidths observed in experiments in which emission is observed from naphthalene with higher rotational energy. To obtain complete coverage of IR wavelengths relevant to the unidentified infrared bands (UIRs), UV laser-induced desorption was used to generate gas-phase highly excited PAHs. Lorentzian band shapes were convoluted with the monochromator-slit function in order to determine the widths of PAH emission bands under astrophysically relevant conditions. Bandwidths were also extracted from bands consisting of multiple normal modes blended together. These parameters are grouped according to the functional groups mostly involved in the vibration, and mean bandwidths are obtained. These bandwidths are larger than the widths of the corresponding UIR bands. However, when the comparison is limited to the largest PAHs studied, the bandwidths are slightly smaller than the corresponding UIR bands. These parameters can be used to model emission spectra from PAH cations and cations of larger PAHs, which are better candidate carriers of the UIRs.
Document ID
Document Type
Reprint (Version printed in journal)
External Source(s)
Cook, D. J.
(University of California Berkeley 94720-1460, United States)
Schlemmer, S.
Balucani, N.
Wagner, D. R.
Harrison, J. A.
Steiner, B.
Saykally, R. J.
Date Acquired
August 21, 2013
Publication Date
February 26, 1998
Publication Information
Publication: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment & general theory
Volume: 102
Issue: 9
ISSN: 1089-5639
Subject Category
Distribution Limits
Non-NASA Center
NASA Discipline Exobiology
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