Two-colour picosecond timeresolved (2 + 1C') resonance enhanced multiphoton ionization photoelectron spectroscopy on the B E1EC'C' and CC' E1AC1E" states of ammonia Dobber, M.R.; Buma, W.J.; de Lange, C.A. Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The picosecond predissociation dynamics of vibronic levels of the B and e' Rydberg states of ammonia have been investigated in real time by (2 + 1') two-color pump-probe ionization in combination with photoelectron spectroscopy. The picosecond real-time results are in reasonable agreement with the results obtained from indirect methods using nanosecond excitation. These indirect methods include investigations of the peak intensities and the natural line widths of the rotational lines in the excitation spectra. The photoelectron spectra obtained for (2 + 1) ionization via the B state in NH3 and ND3 are interpreted and shown to allow for an accurate determination of hitherto unknown vibrational frequencies in the ground state of NH3' (ND3+).For the VI symmetric stretch a frequency of 0.404 f 0.007 eV (0.304 f 0.007 eV) is found, while the frequency of the v4 asymmetric bend vibration has been established as 0.197 f 0.007 eV (0.141 f 0.007 eV). The hydrogen atom fragment, which results from the predissociation of the B and e' Rydberg states, has been detected in a two-color pump-probe experiment using nanosecond excitation.

Resonance enhanced multiphoton ionization photoelectron spectroscopy on nanoand picosecond timescales of Rydberg states of methyl iodide Buma, W.J.; Dobber, M.R.; de Lange, C.A. General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Rydberg states of methyl iodide have been investigated using resonance enhanced multiphoton ionization in combination with photoelectron spectroscopy with nanosecond and picosecond laser pulses. The study of the ns (6~2~ 10) Rydberg states in two-, three-, and four-photon excitations has resulted in an unambiguous identification of state [l] in the 7s and 8s Rydberg states. As a consequence, it is concluded that the transition to 6s [l] in two-and three-photon excitations is anomalously weak. The application of photoelectron spectroscopy to identify the electronic and vibrational nature of a resonance has led to a major reinterpretation of the excitation spectrum of the 6p Rydberg state in two-photon excitation. In many of the recorded photoelectron spectra anomalous electrons are observed, which derive from a one-photon ionization process. This process is suggested to find its origin in the mixing of 6p and 7s character into higher-lying Rydberg states. The major difference between resonance enhanced multiphoton ionization photoelectron spectroscopy with nanosecond and picosecond lasers is found in a less effective dissociation of the molecule in the picosecond experiments. I. INTRODUCTIONThe excited states of methyl iodide have since long attracted considerable interest, both from an experimental and a theoretical point of view.lT31 Investigations of the dissociation occurring in the lowest excited dissociative states, the A band,tm2' and the predissociation of higherlying excited states to the A band23-30 have served as benchmark studies of the dissociation of an isolated molecule. Spectroscopic studies of the Rydberg states of methyl iodide, on the other hand, have allowed for a detailed characterization of properties such as the influence of spinorbit coupling and vibronic interactions,32-35 and the study of analogies of the quantum defects in molecules and rare gas atoms.3"39Methyl iodide is a molecule of C3, symmetry with a ground state electronic configuration . + *aTe4( 'A,). In the following we will, for reasons of convenience, ...

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. The (3+ 1) resonance enhanced multiphoton ionization spectrum of carbon dioxide has been investigated for the (211s3,2,1,2)nf Rydberg states. The excitation spectrum has been obtained for the n =4-13 members, while photoelectron spectra with a resolution of 15 meV have been measured for the ?z =4-7 members. The photoelectron spectra demonstrate that a delicate balance exists between direct and indirect ionization processes as evidenced by the large differences in vibrational activity observed in the spectra obtained via various members of the ("II g3,2,1,2jnf Rydberg series. Strong vibrational activity, which would be forbidden by simple selection rules, is found and interpreted to arise in part from vibronic coupling between various ionic states. Long vibrational progressions, mainly involving the symmetric stretch vibration of the X 211, state of the ion, indicate further severe deviations from Franck-Condon behavior. Two-color excitation of the (2III,s,2, t12)nf Rydberg states provides strong evidence that the superexcited states accessible at the four-photon level have a profound influence on the vibrational progressions and distributions in the photoelectron spectra. Finally, r,esonances associated with multiphoton excitation of atomic carbon and oxygen have been observed. The processes which might be responsible for the occurrence of these atoms are discussed.. 0

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