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

Abstract

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.

Dissociative electron attachment to halogen molecules: Angular distributions and nonlocal effects

“…(9) do not differ substantially from those obtained in Ref. [25] based on the approximation for the capture amplitude, Eq. (1).…”

“…It is known, however, that the Bardsley correction can underestimate DEA cross sections that were indeed observed in Ref. [25]. Moreover, our calculations have shown that the choice a l = l + 1/2 produces cross sections which are substantially smaller than those calculated in Ref.…”

“…Moreover, our calculations have shown that the choice a l = l + 1/2 produces cross sections which are substantially smaller than those calculated in Ref. [25]; therefore, the E 1/2 scaling seems to be more reasonable. While the complete answer to the question about the correction factor requires nonlocal calculations, it is safe to conclude at this point that the present calculations of the integrated cross sections confirm the results of Ref.…”

“…This shows that, in spite of the broken inversion symmetry, resonance scattering in ClF is similar to Cl 2 and F 2 . However, at low energies the s-wave contribution becomes dominant, and this changes the threshold law for DEA [25]. For calculation of the DEA process, the capture amplitude should be expanded in partial waves and connected with the complex parameters γ l .…”

“…The described procedure was applied to K-matrices calculated for e−ClF scattering for five internuclear separation R [25] with the use of the UCL R-matrix code [26][27][28]. The fitting interval was chosen with the center at the resonance position and the range about 2 .…”