Absolute oscillator strengths from<i>K</i>-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\ensuremath{\rightarrow}${\ensuremath{\pi}}^{\mathrm{*}}$ and C 1s\ensuremath{\rightarrow}${\ensuremath{\sigma}}^{\mathrm{*}}$(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.