Dependence upon charge of the vibrational spectra of small Polycyclic Aromatic Hydrocarbon clusters: the example of pyrene★,★★
Laboratoire de Chimie et Physique Quantique (LCPQ/IRSAMC), UMR5626, Université de Toulouse (UPS) and CNRS, 118 Route de Narbonne, 31062 Toulouse, France
2 Laboratoire Collisions Agrégats Réactivité (LCAR/IRSAMC), UMR5589, Université de Toulouse (UPS) and CNRS, 118 Route de Narbonne, 31062 Toulouse, France
a e-mail: email@example.com
Received in final form: 18 July 2020
Accepted: 1 September 2020
Published online: 1 November 2020
Infrared spectra are computed for neutral and cationic clusters of Polycyclic Aromatic Hydrocarbon molecules, namely , using the Density Functional based Tight Binding scheme combined with a Configuration Interaction (DFTB-CI) in the double harmonic approximation. Cross-comparison is carried out with DFT and simple DFTB. Similarly to the monomer cation, the IR spectra of cluster cations are characterized by a depletion of the intensity of the CH stretch modes around 3000 cm−1, with a weak revival for n = 3 and 4. The in-plane CCC modes in the region 1400–2000 cm−1 are enhanced while the CH bending modes in the range 700–1000 cm−1 are significantly weakened with respect to the monomer cation, in particular for n = 2. Finally, soft modes corresponding to diedral fluctuations of the monomers within the central stack of the ion structure, possibly mixed with monomer folding, are also observed in the region 70–120 cm−1.
Contribution to the Topical Issue “Atomic Cluster Collisions (2019)”, edited by Alexey Verkhovtsev, Pablo de Vera, Nigel J. Mason, Andrey V. Solov’yov.
Supplementary material in the form of one pdf file available from the Journal web page at https://doi.org/10.1140/epjd/e2020-10081-0.
© EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020