Absolute oscillator strengths fromK-shell electron-energy-loss spectra of the fluoroethenes and 1,3-perfluorobutadiene

Abstract

Absolute oscillator strengths in the region of carbon and fluorine K-shell excitation have been derived for ${\mathrm{CH}}_2$ ${\mathrm{CH}}_2$, ${\mathrm{CH}}_2$CHF, cis-CHFCHF, ${\mathrm{CH}}_2$ ${\mathrm{CF}}_2$, ${\mathrm{CHFCF}}_2$, ${\mathrm{CF}}_2$ ${\mathrm{CF}}_2$, 1,3-${\mathrm{C}}_4$ ${\mathrm{H}}_6$, and 1,3-${\mathrm{C}}_4$ ${\mathrm{F}}_6$ from electron-energy-loss spectra recorded under dipole-dominated conditions. The methods used to derive absolute oscillator strengths from relative energy-loss intensities are discussed in detail. The accuracy of the procedures is tested through comparisons with literature results for ${\mathrm{N}}_2$, CO, and ${\mathrm{CO}}_2$. The total C 1s→${\pi }^{\mathrm{*}}$ and C 1s→${\sigma }^{\mathrm{*}}$(C—F) intensities increase systematically as the degree of fluorination increases. The spectra are discussed in terms of bond-length correlation and potential barrier concepts.