Experimental studies of cold electron attachment to SF6, CF3Br, and CCl2F2

Garrec, Jean-Luc Le; Sidko, Oleg; Queffelec, J. L.; Hamon, S.; Mitchell, James B.; Rowe, B. R.

doi:10.1063/1.474352

Cited by 59 publications

(59 citation statements)

References 41 publications

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“…Use of such a target offers two substantial advantages: (i) The reaction volume is limited in spatial extent and thereby more easily permits the diagnosis and reduction of residual electric fields in the region of interest; (ii) in supersonic beams, the internal degrees of freedom of a molecule (rotation, vibration) are cooled more or less efficiently [15] and one can thereby investigate cooling effects on the electron attachment processes (which may strongly depend on the vibrational energy [1,2,[16][17][18][19]); in addition electron attachment to clusters can be studied (see, e.g., [19,20]). In the present Letter we address the first point.…”

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confidence: 99%

Laser Photoelectron Attachment to Molecules in a Skimmed Supersonic Beam: Diagnostics of Weak Electric Fields and Attachment Cross Sections Down to20μeV

et al. 1998

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Combining a tunable single mode laser -atomic beam photoelectron source with a skimmed supersonic beam target we have carried out ultrahigh resolution studies of threshold electron attachment to SF 6 molecules. Monitoring SF 6 2 formation around the onset for field ionization of high n Rydberg atoms, residual electric fields are diagnosed and reduced to levels around 0.01 V͞m, allowing the first study of free electron attachment cross sections s͑E͒ for energies down to about 20 meV at energy widths as low as 20 meV. The present results for SF 6 2 production conclusively demonstrate the convergence towards the limiting s-wave attachment behavior s~E 21͞2 at energies below 1 meV.[S0031-9007(98)06711-8] PACS numbers: 34.80.Lx, 34.60. + z, 82.30.Fi The attachment of slow electrons to molecules(1) with formation of long-lived negative ions XY 2 or dissociated products X 2 1 Y (dissociative attachment) is an important process in gaseous dielectrics [1,2]. Many halogen-containing molecules such as SF 6 and CCl 4 exhibit very large electron attachment cross sections at low energies, and it is of both fundamental and applied interest to study the threshold behavior ͑E ! 0͒ with high resolution. For sufficiently short-ranged interaction potentials ͓V ͑r͒~r 2m , m . 2͔, capture of particles with orbital angular momentum L is theoretically predicted to exhibit a threshold energy dependence s͑E͒~E L21͞2 [3,4]. For s-wave attachment ͑L 0͒ one therefore expects a diverging cross section s͑E; L 0͒~E 21͞2ỹ 21 , as also observed for neutron capture by nuclei at low velocities y [3]. Using a vacuum ultraviolet photoelectron attachment technique with an energy resolution around DE ഠ 6 meV (FWHM) Chutjian and coworkers provided evidence for s-wave attachment to occur in several systems including SF 6 and CCl 4 [2,5]. Electron transfer studies with laser excited, state selected Rydberg atoms A ‫ءء‬ ͑nl͒, most notably those by Dunning and colleagues [6,7], demonstrated that the rate coefficient for Rydberg electron attachment ͓ f nl ͑y͒ velocity distribution of nl Rydberg electron͔is essentially constant at high principal quantum numbers ͑n . 40͒ for several molecules including SF 6 and CCl 4 as expected for s-wave attachment. Using a novel laser photoelectron attachment (LPA) method, Klar et al. investigated free electron attachment processes with sub-meV resolution [8][9][10][11]. Their results clearly indicated that the limiting E 21͞2 dependence is reached only at very low energies ͑#1 meV͒; moreover, they detected cusp structures at onsets for vibrational excitation [8,9].At these low energies the major problem is associated with the influence of residual electric fields in the reaction volume. Klar et al. [9,10]-using time-delayed ion extraction following pulsed electron attachment at high repetition rate-carried out model calculations for the effective energy dependence of negative ion formation, taking into account the effects of a homogeneous residual field (of fitted strength) on the electron trajectories. In this way they...

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confidence: 99%

Laser Photoelectron Attachment to Molecules in a Skimmed Supersonic Beam: Diagnostics of Weak Electric Fields and Attachment Cross Sections Down to20μeV

et al. 1998

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“…This lifetime is found to be insensitive to the electron energy, ⑀, over the range 0-100 meV, with an average value of 19.1Ϯ2.7 s. Le Garrec et al 17 have pointed out such a trend in the electron attachment rate coefficient by comparing their measurements performed under thermodynamical equilibrium with results from single collision techniques. In this last case, only the electron temperature ͑correlated to electron energy͒ varies, the neutral temperature remaining constant at 300 K. This was interpreted by the authors as being the result of an individual rate coefficient assigned to each vibrational state of the neutral molecule.…”

Section: Discussionmentioning

confidence: 91%

Measurement of the autodetachment lifetime of SF6−* as a function of electron energy in a free jet expansion

Garrec

Steinhurst

Smith

2001

The Journal of Chemical Physics

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A pure SF6 free jet expansion has been used for the measurement of the autodetachment lifetime of the resonant excited anion SF6−* as a function of electron energy in the range 0–100 meV. In this low temperature environment, the lifetime was found to be 19.1±2.7 μs and independent of electron energy. This result is consistent with earlier statistical modeling of this process in terms of a coupling to the bath of SF6− states which is only a smoothly varying function across the energy range spanned by the electron affinity plus the small variation in electron kinetic energy. The temperature dependence of the autodetachment lifetime also suggests a strong coupling of vibrational motion in SF6 with the autodetachment process consistent with the picture of nuclear excited Feshbach resonances. In addition, the rate coefficient for the very inefficient secondary stabilization rate of the SF6−* states on collision with SF6 neutrals below 10 K is determined to be 3±1×10−12cm3 s−1.

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“…The electron density can be monitored easily by a Langmuir probe and the produced anions by a moveable mass spectrometer. Nitrogen was known to be very efficient at relaxing electrons towards the flow temperature [61] and was therefore used as the buffer. However, careful studies [62] have shown that, in this experiment, the electrons relax to a temperature higher than that in the flow.…”

Section: Electron Attachmentmentioning

confidence: 99%

Gas phase reactive collisions, experimental approach

Canosa

2011

EPJ Web of Conferences

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Abstract. Since 1937 when the first molecule in space has been identified, more than 150 molecules have been detected. Understanding the fate of these molecules requires having a perfect view of their photochemistry and reactivity with other partners. It is then crucial to identify the main processes that will produce and destroy them. In this chapter, a general view of experimental techniques able to deliver gas phase chemical kinetics data at low and very low temperatures will be presented. These techniques apply to the study of reactions between neutral reactants on the one hand and reactions involving charge species on the other hand.

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Experimental studies of cold electron attachment to SF6, CF3Br, and CCl2F2

Cited by 59 publications

References 41 publications

Laser Photoelectron Attachment to Molecules in a Skimmed Supersonic Beam: Diagnostics of Weak Electric Fields and Attachment Cross Sections Down to20μeV

Laser Photoelectron Attachment to Molecules in a Skimmed Supersonic Beam: Diagnostics of Weak Electric Fields and Attachment Cross Sections Down to20μeV

Measurement of the autodetachment lifetime of SF6−* as a function of electron energy in a free jet expansion

Gas phase reactive collisions, experimental approach

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