Absolute cross section measurements for the scattering of low- and intermediate-energy electrons from PF3. I. Elastic scattering

Abstract

We report absolute elastic differential cross sections (DCSs) for electron collisions with phosphorus trifluoride, PF, molecules (e + PF) in the impact energy range of 2.0-200 eV and over a scattering angle range of 10°-150°. Measured angular distributions of scattered electron intensities were normalized by reference to the elastic DCSs of He. Corresponding integral and momentum-transfer cross sections were derived by extrapolating the angular range from 0° to 180° with the help of a modified phase-shift analysis. In addition, due to the large dipole moment of the considered molecule, the dipole-Born correction for the forward scattering angles has also been applied. As a part of this study, independent atom model calculations in combination with screening corrected additivity rule were also performed for elastic and inelastic (electronic excitation plus ionization) scattering using a complex optical potential method. Rotational excitation cross sections have been estimated with a dipole-Born approximation procedure. Vibrational excitations are not considered in this calculation. Theoretical data, at the differential and integral levels, were found to reasonably agree with the present experimental results. Furthermore, we explore the systematics of the elastic DCSs for the four-atomic trifluoride molecules of XF (X = B, N, and P) and central P-atom in PF, showing that, owing to the comparatively small effect of the F-atoms, the present angular distributions of elastic DCSs are essentially dominated by the characteristic of the central P-atom at lower impact energies. Finally, these quantitative results for e - PF collisions were compiled together with the previous data available in the literature in order to obtain a cross section dataset for modeling purposes. To comprehensively describe such a considerable amount of data, we proceed by first discussing, in this paper, the vibrationally elastic scattering processes whereas vibrational and electronic excitation shall be the subject of our following paper devoted to inelastic collisions.

Absolute cross section measurements for the scattering of low- and intermediate-energy electrons from PF3. II. Inelastic scattering of vibrational and electronic excitations

“…As shown in Fig. 2, the first double peak, in the 7.4-8.6 eV ∆E range fitted by two Gaussian functions, corresponds to the 8a 1 1 → 7e (σ * ) transition band, which is split due to the Jahn-Teller effect. 6 The next energy loss feature, from 8.6 to 10.3 eV, has been fitted by a single Gaussian function and represents the broad band with 24 vibrational progressions corresponding to the 8a 1 1 → 4s Rydberg and/or 9a 1 virtual valence excitations.…”

“…The experimental setup and procedure have been described in detail in Ref. 1. For the inelastic electron collision measurements, the original high-resolution spectrometer consisting of a hemispherical monochromator and a similar analyser, computer-controlled lens voltages, and differential pumping have been used.…”

“…7. Furthermore, absolute inelastic cross sections for the low-lying optically allowed 8a 1 1 → 7e (σ * ) excitation band, assigned as the a) Author to whom correspondence should be addressed: masami-h@sophia. ac.jp.…”

“…Jahn-Teller splitting, and 8a 1 1 → 4s Rydberg transitions, 6 were measured at impact energies of 100, 200, and 300 eV for scattering angles ranging from 1.0 • to 15 • . From these results, along with a generalized oscillator strength (GOS) analysis, we derived the oscillator strength f 0 -values and the binary-encounter-f (BEf )-scaled ICSs 8 over a wide energy region, from the excitation threshold to 5000 eV.…”

“…Finally, we estimate our experimental total cross sections below 10 eV by adding the sum of the vibrational inelastic cross sections (v 1 + v 2 + v 3 + v 4 ) to the elastic ICS 1 and compare the present electronic excitation cross sections with the total inelastic ICS calculated by the independent atom model with the screening corrected additivity rule (IAM-SCAR) method above the threshold. Here, the fundamental vibrational modes, v 1 , v 2 , v 3 , and v 4 , correspond to symmetric stretching (110.6 meV), symmetric deformation (60.4 meV), degenerated stretching (106.6 meV), and degenerated deformation (42.7 meV), respectively. 9 In Sec.…”