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.
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, ...
The strong electronic absorption systems of the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands can be used to probe possible mass-variation effects on a cosmological time scale from spectra observed at high redshift, not only in H 2 but also in the second most abundant hydrogen isotopomer HD. High resolution laboratory determination of the most prominent HD lines at extreme ultraviolet wavelengths is performed at an accuracy of = 5 10 ÿ8 , forming a database for comparison with astrophysical data. Sensitivity coefficients K i d ln i =d ln are determined for HD from quantum ab initio calculations as a function of the proton-electron mass ratio . Strategies to deduce possible effects beyond first-order baryon/lepton mass ratio deviations are discussed. DOI: 10.1103/PhysRevLett.100.093007 PACS numbers: 33.20.ÿt, 06.20.Jr, 95.30.Dr, 98.80.Bp The observation of spectral features at high redshift (z 2-3) provides an opportunity to probe minute variations of some fundamental constants over time intervals of 10 10 years, corresponding to 80% of the lifetime of the Universe. For the fine structure constant evidence has been reported for a temporal drift at 5 significance . Variation of another fundamental constant, the dimensionless proton-electron mass ratio m p =m e , may be probed through spectra of molecules. Recently, an indication for a possible decrease of was reported at = 2:45 0:59 10 ÿ5 over a time interval of 12 10 9 years [2,3]. This result is derived from a set of 76 H 2 spectral lines in two absorption systems at z 2:59 and z 3:02 in the line of sight towards quasars Q0405 ÿ 443 and Q0347 ÿ 383 . From observations of the NH 3 inversion splitting in the astrophysical object B0218 357 at z 0:68, a tight constraint upon variation at = 0:6 1:9 10 ÿ6 was deduced . These seemingly contradictory results might be reconciled by invoking the concept of a phase transition having occurred at z 1, transiting from a matter-dominated to a darkenergy-dominated Universe; variation of constants is hypothesized to occur only before the phase transition, henceThe comparison of spectral lines over cosmological time scales depends on the availability of spectral transitions that can be observed at high accuracy and at high redshift. Molecular hydrogen is the most abundant molecule in the Universe by orders of magnitude. The abundance of the deuterated HD species competes with other abundant molecules such as CO and CH such that it is worthwhile to consider the opportunity of using HD absorption for probing mass-variation effects. HD lines in the Lyman bands have indeed been observed in the object Q1232 082 at z 2:34 .To facilitate this opportunity, a set of highly accurate zero-redshift (laboratory) transition wavelengths of HD electronic absorption lines is required. Here we report on the spectral calibration of zero-redshift HD lines in the B 1 u ÿ X 1 g Lyman and the C 1 u ÿ X 1 g Werner bands, referred to as Lv and Wv bands with v the vibrational quantum number, in the extreme ultraviolet range 100-11...
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