Studies of unoccupied orbitals of BF₃ and BCL₃ by electron transmission spectroscopy and multiple scattering Xα calculations

Abstract

Electron transmission spectroscopy (ETS) and bound-state and continuum multiple-scattering X a (MS-Xa) calculations are employed to characterize the unoccupied a;, a; and e' orbitals of BF, and BCI,. The a; orbital of BF,, which produces a peak about 7 eV below threshold in the x-ray absorption spectrum (XAS), generates a scattering resonance at 3.5 eV in ETS. Similarly, the e' orbital that lies about 2 eV above threshold in XAS occurs about 13-16 eV above threshold in ETS. Dissociation of F-from BF, due to electron attachment is attributed to a core-excited shape resonance involving an e" 4 a; excitation and electron capture into the a; orbital. In BCI, all the unoccupied orbitals lie at lower energy than in BF, and are closely spaced, making definitive spectral assignments difficult. Both Hartree-Fock (HF) and M S -X~ methods apparently underestimate the stability of the unoccupied e' orbital of BCI,. Vibronic coupling due to out-of-plane bending may significantly affect the spectral intensities. Feshbach resonances are observed for BCI, at energies close. to those observed in the vacuum-uv absorption spectrum. The lower energies of the unoccupied orbitals of BCI, are consistent with their stronger bonding to nucleophiles.

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

“…As discussed briefly above, the feature at 3.8 eV was confirmed at fairly close energy of 3.54 eV in the ETS of Tossel et al, 12 whereas the weak structures in the total cross section from 6 to 14 eV were not reproduced in such ETS experiments. In addition to the ETS, multiple Xα-calculation was carried out to clarify these experimental resonances in which the unoccupied a 2 ′′ , a 1 ′ , and e ′ orbitals were assumed to generate the resonances at 3.5 and 13-16 eV, respectively.…”

“…ciative electron attachments, [6][7][8] grand total cross section (TCS) measured by Szmytkowski et al, 9 and calculated ionization and TCS with an independent atom model by Vinodkumar et al 10 Angular differential-vibrational excitation of BF 3 for symmetry stretching v 1 and degenerate stretching v 3 modes were reported as a function of the electron energy with a crossed-beam method by Tronc et al 11 As far as elastic differential cross sections (DCSs) and integral cross sections (ICSs) are concerned, we note a few theoretical studies on multi-scattering Xα-calculation of the unoccupied a ′′ 2 , a ′ 1 , and e ′ molecular orbitals of BF 3 and BCl 3 by Tossel et al 12 which are compared with electron transmission spectroscopy (ETS) measurements as well as R-matrix calculations by Radmilović-Radjenović 13 on the elastic scattering and electronic excitation of BF 3 by low energy electrons. 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.…”

“…Such agreement contrasts with other calculations. [12][13][14] Furthermore, Fig. 7(a) shows the inelastic ICSs for degenerate stretching, v 3 mode and composed (v 1 + v 2 + v 4 ) modes together with the total inelastic ICSs from the present IAM-SCAR calculations.…”

Electron Interactions With BCl3

“…27 The lowest unoccupied molecular orbital of the BCl 3 molecule is 2a 2 Љ(B 2p -Cl 3p*), and the next two higher-lying empty orbitals are 3a 1 Ј and 4eЈ (B 2p -Cl 3p*). 29,30 The presence of these unoccupied molecular orbitals helps explain the observed negative ion states of the BCl 3 molecule, and consequently the observed or calculated structure in the electron scattering and electron attachment cross sections. A detailed calculation by Baeck and Bartlett 29 -optimizing bond lengths and bond angles within D 3h symmetry for BCl 3 and C 3v symmetry for BCl 3 Ϫ -provided a number of structural and electronic parameters such as ionization energies, electronic vertical excitation energies, and vibrational frequencies for the BCl 3 , BCl 3 Ϫ , BCl 3 ϩ species.…”

“…4. Figure 4͑a͒ shows the e,partial (⑀) calculated by Tossell et al 30 using the multiple scattering X␣ method. These results show the symmetry of the resonances which give rise to the peaks in the total elastic electron scattering cross section ͑see also Table 3͒.…”