Modeling the infrared cascade spectra of small PAHs: the 11.2 μm band

Cameron J Mackie; Alessandra Candian; Timothy J Lee; Alexander G G M Tielens

doi:10.1007/s00214-021-02807-z

Modeling the infrared cascade spectra of small PAHs: the 11.2 μm band

Theor Chem Acc. 2021;140(9):124. doi: 10.1007/s00214-021-02807-z. Epub 2021 Aug 13.

Authors

Cameron J Mackie^{1

2}, Alessandra Candian³, Timothy J Lee⁴, Alexander G G M Tielens^{5

6}

Affiliations

¹ Kenneth S. Pitzer Center for Theoretical Chemistry Department of Chemistry, University of California, Berkeley, CA 94720 USA.
² Lawrence Berkeley National Laboratory, Chemical Sciences Division, Berkeley, CA 94720 USA.
³ van 't Hoff Institute for Molecular Science, University of Amsterdam, P.O. Box 94157, 1090 GD Amsterdam, The Netherlands.
⁴ NASA Ames Research Center, Moffett Field, CA 94035-1000 USA.
⁵ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
⁶ Astronomy Department, University of Maryland, College Park, MD 20742 USA.

Abstract

The profile of the 11.2 μm feature of the infrared (IR) cascade emission spectra of polycyclic aromatic hydrocarbon (PAH) molecules is investigated using a vibrational anharmonic method. Several factors are found to affect the profile including: the energy of the initially absorbed ultraviolet (UV) photon, the density of vibrational states, the anharmonic nature of the vibrational modes, the relative intensities of the vibrational modes, the rotational temperature of the molecule, and blending with nearby features. Each of these factors is explored independently and influence either the red or blue wing of the 11.2 μm feature. The majority impact solely the red wing, with the only factor altering the blue wing being the rotational temperature.