Rotational and vibrational lifetime of isotopically asymmetrized homonuclear diatomic molecular ions

Amitay, Zohar; Zajfman, D.; Forck, P.

doi:10.1103/physreva.50.2304

Cited by 77 publications

(55 citation statements)

References 24 publications

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“…The cooling rate and the resulting population distribution finally reached are determined by the interaction with the blackbody radiation field of 300 K that pervades the inner volume of the room-temperature ion storage ring, and by the continuous interaction of the HD + ions with the electrons of the electron cooler and the electron target. While the Einstein coefficients between the rotational states required to describe the interaction of HD + with the radiation field are well known [35], the expected large inelastic cross sections for low-energetic electron scattering on rotational states of HD + could only recently be verified by observing the rotational cooling of HD + by super-elastic electron collisions (SEC) in a dedicated experiment [23]. Based on these findings we estimated the time development of the rotational populations by adjusting the calculations described by Shafir et al [23] to the present experimental situation.…”

Section: Resultsmentioning

confidence: 99%

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

et al. 2011

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The collision-energy resolved rate coefficient for dissociative recombination of HD + ions in the vibrational ground state is measured using the photocathode electron target at the heavy-ion storage ring TSR. Rydberg resonances associated with ro-vibrational excitation of the HD + core are scanned as a function of the electron collision energy with an instrumental broadening below 1 meV in the low-energy limit. The measurement is compared to calculations using multichannel quantum defect theory, accounting for rotational structure and interactions and considering the six lowest rotational energy levels as initial ionic states. Using thermal equilibrium level populations at 300 K to approximate the experimental conditions, close correspondence between calculated and measured structures is found up to the first vibrational excitation threshold of the cations near 0.24 eV. Detailed assignments, including naturally broadened and overlapping Rydberg resonances, are performed for all structures up to 0.024 eV. Resonances from purely rotational excitation of the ion core are found to have similar strengths as those involving vibrational excitation. A dominant low-energy resonance is assigned to contributions from excited rotational states only. The results indicate strong modifications in the energy dependence of the dissociative recombination rate coefficient through the rotational excitation of the parent ions, and underline the need for studies with rotationally cold species to obtain results reflecting low-temperature ionized media.

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Section: Resultsmentioning

confidence: 99%

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

et al. 2011

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“…Based on the potential energy curve [20] f ) for rovibrational transitions connecting initial (i) and final (f ) rovibrational levels; the same approach and approximations as in Ref. [44] were used [45]. Since the spin-rotational interaction is negligible, the rotational quantum numbers are J = 0, 1, 2, .…”

Section: Radiative Thermalizationmentioning

confidence: 99%

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

et al. 2005

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The dissociative recombination (DR) of 3 He 4 He + has been investigated at the heavy-ion Test Storage Ring (TSR) in Heidelberg by observing neutral products from electron-ion collisions in a merged beams configuration at relative energies from near-zero (thermal electron energy about 10 meV) up to 40 eV. After storage and electron cooling for 35 s, an effective DR rate coefficient at nearzero energy of 3 × 10 −9 cm 3 s −1 is found. The temporal evolution of the neutral product rates and fragment imaging spectra reveals that the populations of vibrational levels in the stored ion beam are non-thermal with fractions of ∼0.1-1% in excited levels up to at least v = 4, having a significant effect on the observed DR signals. With a pump-probe-type technique using DR fragment imaging while switching the properties of the electron beam, the vibrational excitation of the ions is found to originate mostly from ion collisions with the residual gas. Also, the temporal evolution of the DR signals suggests that a strong electron induced rotational cooling occurs in the vibrational ground state, reaching a rotational temperature near or below 300 K. From the absolute rate coefficient and the shape of the fragment imaging spectrum observed under stationary conditions, the DR rate coefficient from the vibrational ground state is determined; converted to a thermal electron gas at 300 K it amounts to (3.3 ± 0.9) × 10 −10 cm 3 s −1 . The corresponding branching ratios from v = 0 to the atomic final states are found to be (3.7 ± 1.2)% for 1s2s 3 S, (37.4 ± 4.0)% for 1s2s 1 S, (58.6 ± 5.2)% for 1s2p 3 P , and (2.9 ± 3.0)% for 1s2p 1 P . A DR rate coefficient in the range of 2 × 10 −7 cm 3 s −1 or above is inferred for vibrational levels v = 3 and higher. As a function of the collision energy, the measured DR rate coefficient displays a structure around 0.2 eV. At higher energies, it has one smooth peak around 7.3 eV and a highly structured appearance at 15-40 eV. The small size of the observed effective DR rate coefficient at near-zero energy indicates that the electron induced rotational cooling is due to inelastic electron-ion collisions and not due to selective depletion of rotational levels by DR.

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Section: Two-photon Spectroscopy Schemementioning

confidence: 99%

“…The closed set of energy levels coupled by the two-photon spectroscopy scheme is shown in Figure 2. The rovibrational levels have small radiative decay widths, for example Γ3/(2π) = 0.037 Hz and Γ5/(2π) = 13.1 Hz [28]. The parameters used for modelisation are taken from the experimental setups with HD + ions (see for example [17]).…”

Section: Two-photon Spectroscopy Schemementioning

confidence: 99%

THz/Infrared Double Resonance Two-Photon Spectroscopy of HD+ for Determination of Fundamental Constants

Constantin

2017

Atoms

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Abstract:A double resonance two-photon spectroscopy scheme is discussed to probe jointly rotational and rovibrational transitions of ensembles of trapped HD + ions. The two-photon transition rates and lightshifts are calculated with the two-photon tensor operator formalism. The rotational lines may be observed with sub-Doppler linewidth at the hertz level and good signal-to-noise ratio, improving the resolution in HD + spectroscopy beyond the 10 −12 level. The experimental accuracy, estimated at the 10 −12 level, is comparable with the accuracy of theoretical calculations of HD + energy levels. An adjustment of selected rotational and rovibrational HD + lines may add clues to the proton radius puzzle, may provide an independent determination of the Rydberg constant, and may improve the values of proton-to-electron and deuteron-to-proton mass ratios beyond the 10 −11 level.

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Rotational and vibrational lifetime of isotopically asymmetrized homonuclear diatomic molecular ions

Cited by 77 publications

References 24 publications

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

Assignment of resonances in dissociative recombination of HD+ions: High-resolution measurements compared with accurate computations

Dissociative recombination and low-energy inelastic electron collisions of the helium dimer ion

THz/Infrared Double Resonance Two-Photon Spectroscopy of HD+ for Determination of Fundamental Constants

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