D. Bessis

Generalized oscillator strengths for the vibronic excitation levels of the b 1πu electronic state of N2

Abstract The limiting behavior of the recently measured generalized oscillator strengths for the individual vibronic excitation levels ( v ′ = 1–4) of the b 1 π u electronic state of N 2 at 300 eV electron-impact energy is investigated using various theoretical methodologies. From the excellent agreement between the measurement and the universal formula, we conclude that dynamic effects are insignificant at small scattering angles. The new momentum dispersion formula suggests that the 4-term Lassettre fitting formula is optimal for the four measured transitions and produces optical oscillator strengths that are compatible with those of the experiment.

Generalized oscillator strengths for SF6 in the S 2p inner-shell region

Abstract The extrapolation to the optical oscillator strengths (OOSs) of the recently measured small-angle, θ ⩽ 10° generalized oscillator strengths (GOSs) for SF 6 in the S 2p inner-shell region at 1400 eV impact energy has been investigated using various theoretical approaches. These methods include the recent momentum dispersion formula which has the more reliable larger scattering angle measurements embedded in it, the universal formula and the Lassettre fitting formula. From the comparison between the measurements and the universal formula, it is concluded that dynamic effects are less significant for the T 1u (a 1g ) state for θ ⩽ 8°, but are important for the T 1u (t 2g ) and T 1u (e g ) states. We further conclude that the extrapolated OOSs depend sensitively upon the method of extrapolation. The momentum dispersion method produces extrapolated OOS values that are consistent with those of the experiment, thereby manifesting the importance of the accuracy of the larger scattering angle measurements in the extrapolation.

Novel theoretical approaches to small-angle electron scattering

Abstract The difficulties of obtaining reliable measurements of the electron differential cross sections (DCSs) for atomic, ionic and molecular transitions at and near zero scattering angles are well documented. Hence, the need for reliable theoretical calculations. Recently, three theoretical approaches have been derived to investigate and guide measurements of small-angle, including zero, electron DCSs in atoms, ions and molecules. The first method, the momentum dispersion method (MDM), based on Regge Pole theory, uses the analytical continuation of the generalized oscillator strength (GOS) function to obtain the smaller angle, including zero, data from the more reliably measured larger angular data. The second method, the forward scattering function (FSF), represents a unique path of the GOS function to the OOS. It is therefore useful for normalizing the measured relative electron DCSs through the GOSs. Very recently, a singular behavior has been found in the electron–atom scattering DCS at small momentum transfer, K coming from second-order terms and a new generalized Lassettre expansion has been derived. At forward scattering, it is expected to yield the unique long sought after curve that normalizes the measured relative electron DCSs to the OOSs. The utility of the methodologies is demonstrated using atomic, ionic and molecular transitions.