Formation and fragmentation dynamics of superexcited molecules

Abstract: A series of experimental studies on superexcited smallmolecules have been performed giving new information on theformation and fragmentation dynamics of small superexcitedmolecules. Highly monochromatized synchrotron radiation hasbeen applied in the 5-30 eV energy region, corresponding tovalence shell excitation, and in the 60-600 eV region,corresponding to core shell excitation, to reach these neutralstates above the ionization potential.The superexcited states in the irradiated N2and CO and molecules have been probed in thevalence excitation region by detecting dispersed fluorescencewith vibrational resolution emitted from subsequently producedfragments using a liquid nitrogen cooled CCD detector togetherwith a grating spectrometer. The measurements have resulted inthe discovery of non-Rydberg doubly excited resonances. Thesestates are reached directly by simultaneous promotion of twovalence electrons to in space close lying orbitals or viapotential curve crossings. The experimental results have beencomparedwith the results from extensive calculations.A time-of-flight mass spectrometer has been built and usedto measure branching ratios and kinetic energy distributions ofionic fragments produced from molecules in core excited valenceand Rydberg states. The measurements have been performed on CO,OCS and CS2molecules using different coincidence and angularresolved techniques. The results include new information on thegeometry and fragmentation dynamics of these highly excitedmolecules. Monte Carlo simulations have been performed tointerpret some of the data suggesting new models for thefragmentation dynamics. Strong evidences for state and siteselectivity in the fragmentation dynamics of core excitedmolecules have been obtained.