178 research outputs found
Circular dichroism in photoelectron angular distributions from twoâcolor (1+1) REMPI of NO
A detailed experimental and theoretical study of dichroic effects in photoelectron angular distributions is reported for (1+1), twoâcolor REMPI of NO via the A^â2ÎŁ^+, v=0 state. Optically aligned A state rotational levels are probed through ionization by circularly polarized light. Resultant photoelectron angular distributions exhibit significant leftâright asymmetry, the phase and magnitude of which are shown to be related to the curvature of the excited state M_J distribution. Theoretical calculations involving a full ab initio treatment of the ionization dynamics result in circularly dichroic angular distribution (CDAD) parameters in good agreement with those derived experimentally. Additional effects including hyperfine depolarization and coherence are also discussed in relation to the observed CDAD data
Zero kinetic energy-pulsed field ionization and resonance enhanced multiphoton ionization photoelectron spectroscopy: Ionization dynamics of Rydberg states in HBr
The results of rotationally resolved resonance enhanced multiphoton ionization photoelectron spectroscopy and zero kinetic energyâpulsed field ionization studies on HBr via various rotational levels of the F^â1Î_2 and f^â3Î_2 Rydberg states are reported. These studies lead to an accurate determination of the lowest ionization threshold as 94â098.9±1 cm^(â1). Observed rotational and spinâorbit branching ratios are compared to the results of ab initio calculations. The differences between theory and experiment highlight the dominant role of rotational and spinâorbit interactions for the dynamic properties of the highân Rydberg states involved in the pulsed field ionization process
Photoelectron spectroscopy of excited molecular states
Results of studies of ion rotational and vibrational distributions for resonance enhanced multiphoton ionization are discussed
Rotationally resolved photoelectron spectra in resonance enhanced multiphoton ionization of Rydberg states of NH
Results of combined theoretical and experimental studies of photoelectron spectra resulting from (2+1) resonance enhanced multiphoton ionization (REMPI) via the f ^1Î (3pÏ), g ^1Î(3pÏ), and hâ^1ÎŁ^+(3pÏ) Rydberg states of NH are reported. The overall agreement between these calculated and measured spectra is encouraging. Strong ÎN=N+âNâ=even peaks, particularly for ÎN=0, are observed in these spectra. Lowâenergy Cooper minima are predicted to occur in the l=2 wave of the kÏ(^1ÎŁ^+), kÏ(^1ÎŁ^â), and kÏ(^1Î) photoelectron channels for the f state, the kÏ(^1Î), kÎŽ(^1Î ), and kÎŽ(^1Ί) channels for the g state, and the kÏ(^1ÎŁ^+) and kÎŽ(^1Î ) channels for the h state of NH. Depletion of the d wave (l=2) contributions to the photoelectron matrix element in the vicinity of these Cooper minima subsequently enhances the relative importance of the odd lâ waves. The observed ÎN transitions are also affected by strong lâ mixing in the electronic continuum induced by the nonspherical molecular potential. Interference of continuum waves between degenerate ionization channels also determines the spectral pattern observed for photoionization of the fâ^1Î state of NH. Photoelectron angular distributions and the angular momentum compositions of photoelectron matrix elements provide further insight into the origin of these Cooper minima
Breakdown of the Two-Step Model in K-Shell Photoemission and Subsequent Decay Probed by the Molecular-Frame Photoelectron Angular Distributions of CO_2
We report results of measurements and of Hartree-Fock level calculations of molecular-frame photoelectron angular distributions (MFPADs) for C 1s photoemission from CO2. The agreement between the measured and calculated MFPADs is on average reasonable. The measured MFPADs display a weak but definite asymmetry with respect to the O+ and CO+ fragment ions at certain energies, providing evidence for an overlap of gerade and ungerade final ionic states giving rise to a partial breakdown of the two-step model of core-level photoionization and its subsequent Auger decay
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