Candian, A.

Petrignani, A.

Rapacioli, M.

Wiersma, S.D.

English

We present the experimental InfraRed Multiple Photon Dissociation (IRMPD) spectrum and fragmentation mass spectrum of the irregular, cationic PAH dibenzo[a,l]pyrene (C24H+14) in the 6–40 μm/250–1650 cm−1 range. The use of the Free-Electron Laser for IntraCavity Experiments (FELICE) enabled us to record its Far-InfraRed (FIR) spectrum for the first time. We aim to understand how irregularity affects the infrared spectrum and fragmentation chemistry of PAHs. Dibenzo[a,l]pyrene is an asymmetric, non-planar molecule, for which all vibrational modes are in principle IR-active. Calculated harmonic Density Function Theory (DFT) and anharmonic Density Functional based Tight Binding Molecular Dynamics (DFTB-MD) spectra show a large wealth of bands, which match the experiment well, but with a few differences. The periphery of the molecule contains several edge geometries, but out of all possible modes in the 11–14 μm out-of-plane CH bending region, only one band at 13.5 μm is prominent. This fact and the richness of the CC stretching range make irregular PAHs a possible contributor to D-class interstellar spectra. The fragmentation mass spectra reveal facile 2H-loss and no [2C, 2H]-loss, which is attributed to the sterically hindered, non-planar cove region, which could protect irregular PAHs from radiation damage

International Migration, Integration and Social Cohesion online publications

IRMPD spectroscopy of a PAH cation using FELICE:The infrared spectrum and photodissociation of dibenzo[a,l]pyrene

https://pure.uva.nl/ws/files/75504645/IRMPD_spectroscopy_of_a_PAH_cation_using_FELICE.pdf

IRMPD spectroscopy of a PAH cation using FELICE:The infrared spectrum and photodissociation of dibenzo[a,l]pyrene

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International Migration, Integration and Social Cohesion online publications