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Title: Molecular ions, Rydberg spectroscopy and dynamics


Ion spectroscopy, Rydberg spectroscopy and molecular dynamics are closely related subjects. Multichannel quantum defect theory is a theoretical approach which draws on this close relationship and thereby becomes a powerful tool for the study of systems consisting of a positively charged molecular ion core interacting with an electron which may be loosely bound or freely scattering.

  1. Laboratoire Aimé Cotton, Université de Paris-Sud, 91405 Orsay (France)
Publication Date:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1642; Journal Issue: 1; Conference: ICCMSE-2010: International Conference of Computational Methods in Sciences and Engineering 2010, Kos (Greece), 3-8 Oct 2010; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States

Citation Formats

Jungen, Ch. Molecular ions, Rydberg spectroscopy and dynamics. United States: N. p., 2015. Web. doi:10.1063/1.4906703.
Jungen, Ch. Molecular ions, Rydberg spectroscopy and dynamics. United States. doi:10.1063/1.4906703.
Jungen, Ch. 2015. "Molecular ions, Rydberg spectroscopy and dynamics". United States. doi:10.1063/1.4906703.
title = {Molecular ions, Rydberg spectroscopy and dynamics},
author = {Jungen, Ch.},
abstractNote = {Ion spectroscopy, Rydberg spectroscopy and molecular dynamics are closely related subjects. Multichannel quantum defect theory is a theoretical approach which draws on this close relationship and thereby becomes a powerful tool for the study of systems consisting of a positively charged molecular ion core interacting with an electron which may be loosely bound or freely scattering.},
doi = {10.1063/1.4906703},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1642,
place = {United States},
year = 2015,
month = 1
  • We have used two-step, two-color excitation to populate high np singlet Rydberg states of molecular hydrogen under electric-field-free conditions. Sub-Doppler resolution is obtained by exciting the X /sup 1/..sigma../sub g//sup +/..-->..E /sup 1/..sigma../sub g//sup +/ two-photon transition with copropagating photons, then further exciting the molecules to high Rydberg states with a narrow-band laser. We have observed transitions to states up to n--90 for the Rydberg series which converge to the two lowest ionization limits. From an analysis of the energies of the observed transitions we have obtained new results for the first two ionization potentials of molecular hydrogen, with themore » highest accuracy reported to date. The new values are 124 417.61 +- 0.07 cm/sup -1/ for parahydrogen and 124 475.94 +- 0.07 cm/sup -1/ for orthohydrogen. Some of the Rydberg states predissociate strongly, apparently due to the influence of perturbing states of low principle quantum number. This is the first observation of such predissociation in Rydberg states of high principle quantum number.« less
  • A combined experimental and theoretical investigation of the role of electronic and nuclear spins in molecular photoionization is reported. Photoionization spectra of autoionizing p Rydberg states belonging to series converging on the X {sup 2}{sigma}{sub g}{sup +}(v{sup +}=0,N{sup +}=3) level of ortho-H{sub 2}{sup +} have been measured in the range of principal quantum number n=50-200 from the long-lived H {sup 1}{sigma}{sub g}{sup +}(v=0,J=3) level. The use of a pulsed near-Fourier-transform-limited laser with a bandwidth of less than 10 MHz resulted in a Doppler-limited linewidth of 25 MHz which sufficed to partially resolve the hyperfine structure of the Rydberg states. Belowmore » n{approx_equal}70, the exchange interaction between the ion core and Rydberg electrons is larger than the hyperfine interactions in the ion core and the observed levels can be understood in terms of Hund's angular momentum coupling case (d). With increasing value of n, the hyperfine interactions in the core lead to a mixing of singlet and triplet characters of the Rydberg states and eventually to a complete decoupling of the Rydberg electron spin from the core spins that results in distinct series converging on the hyperfine components of the ion. Several intermediate coupling cases have been identified and two of them completely characterized. Most interestingly, the total spin angular momentum has been found to be a good quantum number up to n{approx_equal}150 at least, i.e., far beyond the region where the ionic hyperfine structure starts dominating the coupling hierarchy. Multichannel quantum defect theory including nuclear and electron spins has been extended to treat autoionization and predict spectral intensities. The comparison with the experimental spectra has revealed a satisfactory agreement between calculated and measured line positions, linewidths, and intensities and has enabled us to extract, by extrapolation, a more accurate term value for the H {sup 1}{sigma}{sub g}{sup +}(v=0,J=3) level. The calculations have been used to characterize the role of hyperfine, spin-rotational, and pf interactions in rotational autoionization and have revealed a very strong dependence of the autoionization lifetimes of high Rydberg states on the value of the total angular momentum quantum number F.« less
  • We apply the chirped-pulse millimeter-wave (CPmmW) technique to transitions between Rydberg states in calcium atoms. The unique feature of Rydberg-Rydberg transitions is that they have enormous electric dipole transition moments ({approx}5 kiloDebye at n*{approx} 40, where n* is the effective principal quantum number), so they interact strongly with the mm-wave radiation. After polarization by a mm-wave pulse in the 70-84 GHz frequency region, the excited transitions re-radiate free induction decay (FID) at their resonant frequencies, and the FID is heterodyne-detected by the CPmmW spectrometer. Data collection and averaging are performed in the time domain. The spectral resolution is {approx}100 kHz.more » Because of the large transition dipole moments, the available mm-wave power is sufficient to polarize the entire bandwidth of the spectrometer (12 GHz) in each pulse, and high-resolution survey spectra may be collected. Both absorptive and emissive transitions are observed, and they are distinguished by the phase of their FID relative to that of the excitation pulse. With the combination of the large transition dipole moments and direct monitoring of transitions, we observe dynamics, such as transient nutations from the interference of the excitation pulse with the polarization that it induces in the sample. Since the waveform produced by the mm-wave source may be precisely controlled, we can populate states with high angular momentum by a sequence of pulses while recording the results of these manipulations in the time domain. We also probe the superradiant decay of the Rydberg sample using photon echoes. The application of the CPmmW technique to transitions between Rydberg states of molecules is discussed.« less
  • The energy shifts of high-angular-momentum Rydberg states in berylliumlike O{sup 4+}, due to long-range interactions of the Rydberg electron with the ionic core, are measured by laser spectroscopy, using stimulated two-step recombination of free electrons with O{sup 5+} ions. The comparison of the accurate experimental results with theoretical shifts from the core polarization model and from {ital ab} {ital initio} atomic structure calculations shows considerable disagreement, demonstrating the need for an efficient method to include configuration interaction in a long-range interaction model.
  • The high-angular-momentum Rydberg state structure of berylliumlike N3+ has been measured using laser-stimulated two-step recombination spectroscopy. A 65 MeV beam of N4+ ions from the MPI tandem accelerator is stored in the heavy-ion storage ring TSR and is velocity-matched with a colinear electron beam in the electron cooler section of the ring. Intense pulsed lasers stimulate selective electron capture into a high Rydberg state, followed by de-excitation to a specific lower Rydberg level. Results will be reported for weakly-perturbed high angular momentum components of the n=13-8 and n=13-7 transitions in N3+. Comparisons will be presented with previous measurements of low-nmore » Rydberg transitions, with polarization model predictions, and with atomic structure calculations. The extension of the measurements to strongly-perturbed angular momentum states will be discussed.« less