On the validity of the Arrhenius equation for electron attachment rate coefficients

Fabrikant, I. I.; Hotop, H.

doi:10.1063/1.2841079

Cited by 57 publications

(52 citation statements)

References 34 publications

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“…5 over the electron energy distribution. The results do not show a significant temperature dependence because the low-energy behavior of the cross section is close to E −1/2 meaning that the rate coefficient weakly depends on E. The growth of the ClF rate coefficient with temperature is slow and does not indicate any activation energy typical for Arrheniustype behavior [44]. In Fig.…”

Section: Experimental Results and Comparison With Theorymentioning

confidence: 71%

Electron attachment to the interhalogen compounds ClF, ICl, and IBr

et al. 2016

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Thermal electron attachment rate coefficients for three interhalogen compounds (ClF, ICl, IBr) have been measured from 300 to 900 K at pressures of 1-2 Torr using a flowing afterglow-Langmuir probe apparatus. ClF attaches somewhat inefficiently (k = 7.5×10 −9 cm 3 s −1 ) at 300 K, with the rate coefficient rising to 1.7×10 −8 cm 3 s −1 at 700 K. At higher temperatures the apparent rate coefficient falls steeply; however, this is interpreted as an artifact due to decomposition on the walls of the inlet line. ICl attaches with even lower efficiency (k = 9.5×10 −10 cm 3 s −1 at 300 K) and a less steep increase with temperature. Attachment to IBr is too slow to confidently measure with the present experiment, with an upper limit on the rate coefficient of 10 −10 cm 3 s −1 from 300 to 600 K. Both ClF and ICl attach dissociatively to yield Cl − , likely exclusively, though F − or I − may be produced with limits of <2% and <5%, respectively. The ClF attachment was further explored through ab initio calculation of the ClF and ClF − potential energy curves and R-matrix calculations of the resonance parameters which were used then for calculations of the dissociative attachment cross sections and rate coefficients. While the magnitude of the attachment rate coefficient for ClF is similar to those for both Cl 2 and F 2 , the calculated cross sections show qualitatively different threshold behavior due to the s-wave contribution allowed by the lack of inversion symmetry. The v = 1 and 2 vibrational modes of ClF attach about three to four times faster than v = 0 and 3 at energies lower than ∼0.2 eV. The calculated rate coefficients are in good agreement with the experiment at 300 K and increase moderately less steeply with temperature.

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Section: Experimental Results and Comparison With Theorymentioning

confidence: 71%

Electron attachment to the interhalogen compounds ClF, ICl, and IBr

et al. 2016

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“…Ruckhaberle et al 39 supported their low activation energy with density functional calculations on the change in NF 3 potential energy for N-F stretching motion, which yielded an activation energy of 0.2 eV, believed an overestimate. Aside from a question of whether such a calculation is accurate enough to choose between the rival experimental activation energies, there are more important issues noted by Fabrikant and Hotop 44 in a recent study of Arrhenius-like behavior in electron attachment. Fabrikant and Hotop 44 found that the activation energy determined from thermal attachment depended on whether the reaction was endothermic or exothermic.…”

Section: Resultsmentioning

confidence: 97%

A new instrument for thermal electron attachment at high temperature: NF3 and CH3Cl attachment rate constants up to 1100 K

Miller

Friedman

Williamson

et al. 2009

Review of Scientific Instruments

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A new high temperature flowing afterglow Langmuir probe (HT-FALP) apparatus is described. A movable Langmuir probe and a four-needle reactant gas inlet were fitted to an existing high temperature flowing afterglow apparatus. The instrument is suitable for study of electron attachment from 300-1200 K, the upper limit set to avoid softening of the quartz flow tube. We present results for two reactions over extended ranges: NF(3) (300-900 K) and CH(3)Cl (600-1100 K). Electron attachment rate constants for NF(3) had been measured earlier using our conventional FALP apparatus. Those measurements were repeated with the FALP and then extended to 900 K with the HT-FALP. CH(3)Cl attaches electrons too weakly to study with the low temperature FALP but reaches a value of approximately 10(-9) cm(3) s(-1) at 1100 K. F(-) is produced in NF(3) attachment at all temperatures and Cl(-) in CH(3)Cl attachment, as determined by a quadrupole mass spectrometer at the end of the flow tube. Future modifications to increase the plasma density should allow study of electron-ion recombination at high temperatures.

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“…The modeling suggests a larger barrier than does an Arrhenius fit; interestingly, application of Rmatrix theory to other exothermic dissociative electron attachments also suggests that Arrhenius underestimates the barrier height in such systems. 48 The near flat temperature dependence of the rate constant over the measured range is the result of the positive dependence on the C 2 F 5 internal energy distribution being offset by the negative dependence on the electron temperature. At lower temperatures, the former will dominate, and Arrhenius fit behaviour is predicted.…”

Section: Discussionmentioning

confidence: 99%

“…48 The C 2 F 5 data may be fitted to an Arrhenius equation assuming a small activation energy of 90 cm −1 ; corresponding to an energetic barrier between the neutral and anion potential energy surfaces where some amount of vibrational excitation is needed to surmount the barrier. The Arrhenius description tends to fail at higher energies and offers limited physical insight into the magnitude of the rate constants.…”

Section: Discussionmentioning

confidence: 99%

Dissociative electron attachment to C2F5 radicals

Haughey

Field

Langer

et al. 2012

The Journal of Chemical Physics

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Dissociative electron attachment to the reactive C 2 F 5 molecular radical has been investigated with two complimentary experimental methods; a single collision beam experiment and a new flowing afterglow Langmuir probe technique. The beam results show that F − is formed close to zero electron energy in dissociative electron attachment to C 2 F 5 . The afterglow measurements also show that F − is formed in collisions between electrons and C 2 F 5 molecules with rate constants of 3.7 × 10 −9 cm 3 s −1 to 4.7 × 10 −9 cm 3 s −1 at temperatures of 300-600 K. The rate constant increases slowly with increasing temperature, but the rise observed is smaller than the experimental uncertainty of 35%.

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On the validity of the Arrhenius equation for electron attachment rate coefficients

Cited by 57 publications

References 34 publications

Electron attachment to the interhalogen compounds ClF, ICl, and IBr

Electron attachment to the interhalogen compounds ClF, ICl, and IBr

A new instrument for thermal electron attachment at high temperature: NF3 and CH3Cl attachment rate constants up to 1100 K

Dissociative electron attachment to C2F5 radicals

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