Dependence upon charge of the vibrational spectra of small Polycyclic Aromatic Hydrocarbon clusters: the example of pyreneLéo Dontot, Fernand Spiegelman, Sébastien Zamith and Mathias RapacioliEur. Phys. J. D, 74 11 (2020) 216DOI: https://doi.org/10.1140/epjd/e2020-10081-0