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Rydberg excited states of the CS 2 molecule in the energy range 56 000-81 000 cm Ϫ1 have been further investigated via the two and three photon resonance enhancements they provide in the mass resolved multiphoton ionization ͑MPI͒ spectrum of a jet-cooled sample of the parent molecule. Spectral interpretation has been aided by parallel measurements of the kinetic energies of the photoelectrons that accompany the various MPI resonances. Thus we have been able to extend, and clarify, previous analyses of the tangled spin-orbit split vibronic structure associated with the

(v , 0) Werner bands for v = 0-4, using a narrow-band tunable extreme UV laser source at wavelengths λ = 92-105 nm in conjunction with the technique of 1 + 1 two-photon ionization. The measurements can be divided into three categories for which varying absolute accuracies were obtained. Special focus was on the B, v = 2-5 bands, where an accuracy of 0.004 cm −1 or δν/ν = 4 × 10 −8 is achieved. For transitions to B, v ≤ 13 and C, v ≤ 3 states the accuracy is 0.005 cm −1 or δν/ν = 5 × 10 −8 . Due to a different frequency mixing scheme uncertainties for B, v ≥ 13 and C, v = 4 are at the level of 0.011 cm −1 or δν/ν = 1.1 × 10 −7 . Inspection of combination differences between R(J ) and P(J + 2) lines shows that the accuracies are even better than estimated in the error budget. Based on the measurements of 138 spectral lines and the known combination differences, transition frequencies of 60 P-lines could be calculated as well, so that a data base of 198 accurately calibrated lines results for the Lyman and Werner bands of H 2 .Key words: vacuum UV, molecular spectroscopy, hydrogen, precision metrology. . Un examen des différences des combinaisons entre les raies R(J ) et P(J + 2) montre que les précisions sont meilleures que celles évaluées dans le budget des erreurs. Sur la base de mesures de 138 raies spectrales et de différences de combinaison connues, on a pu aussi calculer les fréquences de transition de 60 raies P et il en résulte qu'une base de données de 198 raies bien calibrées est disponible pour les bandes de Lyman et de Werner du H 2 .

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.

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