Elastic scattering of low-energy electrons by BF3

Crossed-beam experiment for the scattering of low- and intermediate-energy electrons from BF3: A comparative study with XF3 (X = C, N, and CH) molecules

“…However, forward scattering begins to slightly increase at 3.5 eV, where the angular distribution shows a relatively isotropic behavior. We note that a shape resonance has been reported at ∼3.5 eV with B 2 symmetry of the C 2v group, corresponding to the A ′′ 2 symmetry of the D 3h group as pointed out by Pastega et al 15 Such behavior of the angular distribution has also been observed in the case of T d symmetry molecules such as CCl 4 25 and CF 4 44 at electron impact energies near or above the energy position of the shape resonances. The R-T minimum at 0.7 eV in the A 1 state 15 is outside of the present impact energy region, but the effect can still be clearly observed in the isotropic behavior of the DCS below 3.5 eV, except for smaller scattering angles, i.e., below 40 • .…”

“…3(a)-3(d), we compare our elastic DCSs of BF 3 with those of XF 3 (X = C, 20,21 N, 16 and CH 19 ) molecules together with the IAM-SCAR and the SMC calculations for BF 3 at 4.0, 7.0, 30, and 60 eV. At 4.0 eV, close to the resonance energy in the B 2 symmetry of C 2v group, the DCS for BF 3 has a minimum around 100 • attributed to p-wave-like scattering as pointed out by Pastega et al 15 It is interesting to note that NF 3 DCS shows a similar behavior as BF 3 , whereas for CHF 3 one order of magnitude higher than BF 3 , NF 3 , and CHF 3 molecules albeit with similar DCS shape and local minimum at ∼90 • . The SMC calculations by Diniz et al 45 have shown the similarity between the elastic DCSs of the CF 3 radical and CHF 3 molecules.…”

“…The current elastic DCSs for BF 3 i.e., 1.5-15 eV, the present DCSs can be compared with the recent SMC-SE and SMC-SEP calculations of da Costa et al 14 and Pastega et al, 15 respectively. From the latter study, a better agreement with the present experimental DCS in the electron energy range below 10 eV is obtained except for scattering angles smaller than 40 • .…”

“…In general, vibrational excitation contributes to about a few percent at higher impact energies (above 30 eV), with little influence on the shape of the elastic peak. However, around the RamsauerTownsend (R-T) minimum expected at 1.5 eV, 15 a symmetric stretching vibration (ν 3 ) is normally expected to exceed the elastic cross section. Moreover, both elastic and vibrational excitations are normally enhanced around the shape resonance at 3.8 eV.…”

“…More recently, the Schwinger multichannel (SMC) method was employed in the static-exchange (SE) and the static-exchange-polarization (SEP) approximations in the energy range from 0.1 to 10 eV. 14,15 However, no systematic measurement of the DCS has been reported in a wider electron energy region from low-to intermediateenergy range. The present study, therefore, represents a new and original experimental contribution of the DCS data for BF 3 in the energy range of 1.5-200 eV, which have been compared with similar 3-fluorine atom compounds on elastic-scattering from NF 3 , 16-18 CHF 3 , 19 and CF 3 -radical.…”