Hannover 2003 – scientific programme

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MO: Molekülphysik

MO 6: Poster I

MO 6.6: Poster

Tuesday, March 25, 2003, 16:00–18:30, Lichthof

Unimolecular fragmentation of polycyclic aromatic hydrocarbons — •Adalbert Ding, Christian Lenski, and Michael Lenski — Technische Universität Berlin, Optisches Institut, Sekretariat P1-1, Strasse des 17. Juni 135, 10623 Berlin

Polycyclic aromatic hydrocarbons (PAHs) are supposed to be the carriers of the diffuse interstellar bands (DIB). Most favoured theories concerning the DIB-phenomenon propose that the observed radiation originates from infrared fluorescences of vibronic highly excited PAHs. Photodissociation of PAHs has been shown to be the principal process competing with radiative relaxation of these PAHs. Due to their high resilience towards decomposition PAHs are attractive compounds for photoionization studies.

In the present study light from the Berlin synchrotron BESSY was used to investigate the fragmentation of various PAHs by means of standard ionisation and coincidence techniques.

After having been ionized using photon energies between 10 eV and 30 eV various substances have been analyzed in a McLaren-type time of flight mass spectrometer.

At sufficiently high photon energies the studied PAHs dissociate by splitting off H-atoms and C_xH_y-fragments. The critical energies are determined and compared with appropriate values from electron bombardement ionisation. By means of experimentally taken breakdown curves the isomerisation processes of the studied substances are discussed. At least the breakdown curves mentioned before are compared with RRKM calculations.