Lifetime and electronic state interference and ultrafast dissociation of inner-shell resonant Raman excited CO, NO, CO2, and N2O investigated by photon-induced fragment-fluorescence spectrometry (PIFS)

• Applicant: Professor Dr. Arno Ehresmann
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2008 to 2013
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 66946523

Inner-shell resonance decay processes of molecules after their excitation by synchrotron radiation (electron emission processes, like Auger/double Auger decays or ultrafast dissociative processes, like Coulomb explosion) are prototypes for the test of basic quantum mechanics and are, therefore, the topic of intense current research. In the present project two aspects of these decay processes will be investigated in a fresh experimental approach, where excitation by small bandwidth monochromatized synchrotron radiation is used together with high resolution (dispersed) fragment fluorescence spectrometry and polarimetry (photon-induced fluorescence spectrometry, PIFS) to determine absolute fragment-state selective fragmentation cross sections as functions of the exciting-photon energy: 1) Lifetime vibrational interference (LVI) and electronic state interference (ESI) effects, and 2) ultrafast dissociation. This as yet very scarcely applied experimental approach will be combined with elaborate ab-initio calculations by a co-operating group for a quantitative comparison between experiment and theory. The decays of molecular inner shell resonances are strongly influenced by lifetime vibrational interference (LVI) and electronic state interference (ESI), due to closely neighbouring vibronic or electronic resonant states, overlapping partly within their natural linewidths. PIFS experiments, partly with polarization analysis of the emitted fluorescence, will be used to investigate experimentally LVI and ESI in the inner-shell resonantly excited heteroatomic molecules CO and NO. For these molecules it is possible to compare the decay of inner shell resonances strongly influenced by LVI and ESI effects (excitation of the O1s electron) with the decay of resonances weaker influenced (excitation of the C1s or N1s electron in CO or NO, respectively). Ultrafast dissociation processes of the inner-shell resonances will be investigated by dispersively monitoring the fluorescence emission of excited neutral fragments. These fragments cannot be emitted by the Coulomb explosion mechanism and are an indication of a very fast dissociation process competing with the abundant autoionization mechanisms for the deexcitation of the resonances. Finally, we will start to investigate fragmentation processes of the triatomic molecules CO2 and N2O after vibration-state selective inner-shell excitation of the C1s (N1s) and O1s electrons into molecular excited CO+ (N2+ and NO+) fragments by recording dispersedly CO+ (N2+ and NO+) fluorescence in well-known wavelength ranges, being therefore state-selective to the CO+ (N2+ and NO+) fragment state.

• DFG Programme: Research Grants