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  • Articles: DFG German National Licenses  (4)
  • 2000-2004  (1)
  • 1990-1994  (3)
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  • Articles: DFG German National Licenses  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 908-926 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the singlet gerade Rydberg series with low total angular momentum J=0,1,2 of molecular hydrogen near the ionization threshold. They are excited by starting at selected rotational levels of the B 1Σ+u (v'=0) state. The spectra show Rydberg series converging at the different rovibrational levels of the X 2Σ+g electronic ground state of H+2 with the Rydberg electron in an s or d-electronic orbital. An identification of the final states is done with the help of a model multichannel quantum defect theory (MQDT) calculation, which is also used to calculate quantum defects from a small set of parameters. Nearly n-independent quantum defects are derived from the experiment for the different Rydberg series with the Rydberg electron in the s-orbital. In the d-Rydberg series perturbations through l-uncoupling are small. An electronic s–d interaction between Rydberg series is present, which is partly induced by the doubly excited gerade configuration (1σu)2. Decay processes of the Rydberg states through autoionization, predissociation, or electric field ionization are found in the excitation spectra.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2781-2789 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Gas-phase C60 photoionization and photofragmentation experiments were performed using a sub-50 fs Ti Sapphire laser system and reflectron time-of-flight (RETOF) mass spectrometer. The dependence of the C60+ and C602+ signals on the laser intensity for the fundamental (795 nm) and second harmonic (ca. 400 nm) has been determined. For low laser intensities, before the onset of fragmentation, single ionization is a direct multiphoton process. Double ionization is a sequential process in which C602+ originates from already singly ionized fullerenes. At laser intensities beyond the onset of C602+ there is considerable metastable fragmentation indicating a strong coupling of electronic excitation energy into vibrational degrees of freedom that appears to be in competition with multiple ionization. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0649
    Keywords: 07.60 ; 78.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Surface sum-frequency mixing is shown to be a valuable tool in determining the width and shape of ultrashort ultraviolet and infrared laser pulses. The method is demonstrated to measure UV pulses of 300 fs and IR pulses of about 2.9 ps duration. In cross-correlation set-ups the method is inherently background-free, but background-free arrangements can also be realized for autocorrelation measurements, useful especially in the ultraviolet. In the present experiments on GaAs(111) and Pd(111) a spectral range from 3.3 μm to below 200 nm is covered, which certainly can be extended to longer as well as to shorter wavelengths. Due to the small source volume phase-matching is not required.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 15 (1990), S. 133-139 
    ISSN: 1434-6079
    Keywords: 32.80.Rm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We observe that resonant ionization plays a dominant role in the multiphoton ionization (MPI) of xenon at wavelengths around 600 nm, irrespective of the detuning of multiples of the photon energy from excited states of the undisturbed atom. Angular distributions of energy resolved photoelectrons allow to identify excited states which are strongly ac-Stark shifted in the intense laser field and which serve as intermediate resonances in MPI processes. Angular distributions measured at different wavelengths show that the ac-Stark shift of excited states can be larger than the photon energyhω. Our results support the model proposed by Freeman et al.
    Type of Medium: Electronic Resource
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