Coherent Oscillatory Femtosecond Dynamics in Multichannel Photodynamics of NO2 Studied by Spatially Masked Electron Imaging

400 fs) a second slow (near 0 eV) photoelectron channel is observed that is associated with one photon excitation at 400 nm to the first excited (A) over bar B-2(2) state NO2 followed by two photon excitation at 266 nm leading to near threshould tomization and dissociation to NO- + O(P-3). Distinctive oscillatory patterns were found in the pump-probe transients of the photoelectron yield for both the slow and the fast photoelectron channels but with different periods of about 750 fs (slow) ro 590 fs (fast) Extensive polarization experiments are reported for both linerar and circular polarized pump and probe laser geometries. We discuss the oscillatory mechanism in relation to ab initio calculations of relevant Rydberg and valence type excited states of NO2 near 9.3 eV. We propose that an oscillating wavepacked of mixed Rydberg and valence character that predissociates is reponsible for the observed osicillations in the transients of the fast (0.88 eV) photoelectron channel