Photodetachment microscopy of the P, Q, and R branches of the OH−(v=0) to OH(v=0) detachment threshold

Goldfarb, Fabienne; Drag, Cyril; Chaibi, W.; Kröger, S.; Blondel, Christophe; Delsart, C.

doi:10.1063/1.1824904

Cited by 61 publications

(79 citation statements)

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“…These deviations can be explained by the effect of rotational excitation of the OH − anions. By summing up the Hönl-London factors for photodetachment into all accessible final states [8,27], it turns out that the rotational contribution to the photodetachment cross section is given by a factor proportional to (2J +1), where J is the rotational state of OH − . This leads to a photodetachment cross section ratio for thermal distributions at 0 K, 170 K, 300 K and 850 K of 1:4.3:5.8:9.8.…”

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confidence: 99%

“…The trap is cooled to 170 K, which strongly increases the lifetime of the trapped ions. A focused helium neon laser at 632.8 nm is passed through the trap, which photodetaches OH − (electron affinity 1.83 eV [8]) in a one-photon transition. In the trap ions are stored in a cylindrical structure of 22 stainless steel rods of 40 mm length and 10 mm inscribed diameter, alternatingly connected to the two phases of a radio-frequency oscillator.…”

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Photodetachment of ColdOH−in a Multipole Ion Trap

et al. 2006

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The absolute photodetachment cross section of OH − anions at a rotational and translational temperature of 170 K is determined by measuring the detachment-induced decay rate of the anions in a multipole radio-frequency ion trap. In comparison with previous results, the obtained cross section shows the importance of the initial rotational state distribution. Using a tomography scan of the photodetachment laser through the trapped ion cloud, the derived cross section is model-independent and thus features a small systematic uncertainty. The tomography also yields the column density of the OH − anions in the 22-pole ion trap in good agreement with the expected trapping potential of a large field free region bound by steep potential walls.PACS numbers: 33.80. Eh,33.80.Ps,33.70.Ca,95.30.Ky Photodetachment of the excess electron from a negative ion represents a fundamental light-matter interaction process that reveals detailed information on atomic and molecular structure and dynamics. The additional electron is only bound by virtue of electron-electron interactions and its binding energy often depends sensitively on electron correlations in the entangled multi-electron wavefunction. Spectroscopic information, obtained from photoelectron energy measurements, is used to study the electronic, vibrational and rotational Eigenstate spectrum of anionic and neutral molecules. This also yields insight in transition states structures of reactive collisions of neutral molecules [1]. In addition, ultrafast timeresolved studies of wavepacket or electron rearrangement dynamics inside clusters have employed anion photoelectron spectroscopy [2]. Multiphoton electron detachment in short laser pulses provides information on the electronatom interaction in strong laser fields [3]. Cross sections for photodetachment reveal complementary information to photoelectron spectra and serve to challenge calculations for bound-free transition matrix elements [4].The most detailed photodetachment cross section studies on a molecular anion have been carried out for the hydroxyl anion OH − . Much of the work on OH − has focused on relative cross sections. Near threshold, comparison of the relative cross section as a function of electron energy with Wigner threshold laws allows for precise tests of the long-range electron-neutral interactions. Specifically, the subtle coupling of the two lowest Λ-doublet states has been observed, which leads to a long-range electron-dipole interaction [5,6]. Also, relative cross section measurements for transitions of specific rotational states have been carried out for OH − [7,8]. These results indicate deviations of the photodetachment cross section from s-wave electron detachment calculations. Interpretation, however, is obscured by the incomplete knowledge of the OH − rotational population. Even for the OH − anion only two absolute cross section measurements have been performed to date [9,10], which disagree with each other and deviate from the calculated one by almost an order of magnitude [4].An important ...

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Photodetachment of ColdOH−in a Multipole Ion Trap

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“…p(J, T ) is the population of the rotational level J which weights the cross sections from each state. I Jb are the Hönl-London factors giving the relative transition intensities [21,22]. Θ is the Heaviside function taking only transitions above threshold into account, hν is the photon energy and Ji is the energy threshold of the transition.…”

Section: Theoretical Methodsmentioning

confidence: 99%

Incomplete rotational cooling in a 22-pole ion trap

Endres

Egger

Lee

et al. 2017

Journal of Molecular Spectroscopy

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Cryogenic 22-pole ion traps have found many applications in ion-molecule reaction kinetics and in high resolution molecular spectroscopy. For most of these applications it is important to know the translational and internal temperatures of the trapped ions. Here, we present detailed rotational state thermometry measurements over an extended temperature range for the two ion/buffer gas systems OH − /He and OD − /HD with ion-to-neutral mass ratios of 4.25 and 6 respectively. The measured rotational temperatures show a termination of the thermalisation with the buffer gas around 25 K, independent of mass ratio and confinement potential of the trap. Different possible explanations for this incomplete thermalisation have been investigated, among them the thermalisation of the buffer gas and the heating due to room temperature blackbody radiation and room temperature gas entering the trap.

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“…They are assigned to the openings of the photodetachment transitions R3(0), Q3(1), and P3(2) (for the notation see Ref. 13 ) transitions, which all form neutral OH in the rotational ground state of the 2 Π 3/2 spin-orbit manifold. Thus, the energy difference between the thresholds represents directly the rotational levels in the molecular anion, which are known from rotational spectroscopy 12 to be given by 37.5 cm −1 for the J = 1 ← 0 excitation and 112.3 cm −1 for the J = 2 ← 0 excitation, respectively.…”

Section: Near-threshold Photodetachment Of Oh −mentioning

confidence: 99%

“…13 ) and threshold energies, and p is the exponent for the power law describing the energy dependence of the cross section near threshold. For a non-interacting outgoing s-wave electron p = 0.5, corresponding to the Wigner threshold law.…”

Section: Near-threshold Photodetachment Of Oh −mentioning

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Internal state thermometry of cold trapped molecular anions

Otto

Zastrow

Best

et al. 2013

Phys. Chem. Chem. Phys.

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− 2 anions has been performed in a cryogenic 22-pole radiofrequency multipole trap. Measurements of the detachment cross section as a function of laser frequency near threshold have been analysed. Using this bound-free spectroscopy approach we could demonstrate rotational and vibrational cooling of the trapped anions by the buffer gas in the multipole trap. Below 50 K the OH − rotational temperature shows deviations from the buffer gas temperature, and possible causes for this are discussed. For H 3 O − 2 vibrational cooling of the lowest vibrational quantum states into the vibrational ground state is observed. Its photodetachment cross section near threshold is modelled with a Franck-Condon model, with a detachment threshold that is lower, but still in agreement with the expected threshold for this system.

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Photodetachment microscopy of the P, Q, and R branches of the OH−(v=0) to OH(v=0) detachment threshold

Cited by 61 publications

References 31 publications

Photodetachment of ColdOH−in a Multipole Ion Trap

Photodetachment of ColdOH−in a Multipole Ion Trap

Incomplete rotational cooling in a 22-pole ion trap

Internal state thermometry of cold trapped molecular anions

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