Non-dipole electron impact spectroscopy of a common local anesthetic: Generalized oscillator strengths of valence, Cl 2p and C 1s pre-edge transitions of chloroethane

Abstract

Angle-resolved electron energy loss spectroscopy at 2.5 keV impact energy has been used to determine absolute generalized oscillator strengths (GOSs) of discrete transitions in the pre-edge regions of the valence, Cl 2p and C 1s shells of chloroethane as functions of energy loss and momentum transfer. A new lowest-lying preionization-edge energy-loss feature at 7.2 eV has been clearly identified at a non-zero momentum transfer. The corresponding GOS profile is found to have a shape characteristic of non-dipole transitions that can be attributed to electronic excitations from nonbonding Cl 3p initial-state orbitals (4a″ and 13a′) to antibonding σ* C–Cl final-state orbital (14a′). The GOS profiles of the other low-lying valence-shell and Cl 2p and C 1s pre-edge features are found to have maximum intensity at zero momentum transfer, generally consistent with the spectral assignments to dipole-allowed transitions involving final-state Rydberg orbitals. Differences in and between the GOS profiles for the valence-shell and these inner-shell pre-edge features in C 2H 5Cl are identified. Although no discernible secondary extrema can be found in any of the inner-shell GOS profiles, subtle differences can be observed and are consistent with the proposed assignments. The present GOS results for C 2H 5Cl are compared with the available GOS data reported for other mono-chlorides, including CF 3Cl and CHF 2Cl.