The valence shell photoabsorption of the linear alkanes, C nH 2 n+2 ( n=1–8): absolute oscillator strengths (7–220 eV)

Abstract

The absolute valence shell photoabsorption spectra of the first eight members of the homologous linear (normal) alkane series, CH 4 to C 8H 18, have been obtained from electron energy loss measurements using dipole (e, e) spectroscopy at a resolution of 1 eV fwhm in the equivalent photon energy range 7–220 eV. Absolute oscillator strengths (transition probabilities) for discrete and continuum photoabsorption transitions have been determined throughout the entire energy range. The lower energy regions (7–50 eV) of the spectra have also been studied at high resolution (0.048 eV fwhm), and essentially all the features observed in the discrete excitation region of CH 4, C 2H 6, C 3H 8, and C 4H 10 can be reasonably assigned to Rydberg transitions by using quantum defects and the transferability of term values. The quite good agreement between the present results and the constrained dipole oscillator strength distribution (DOSD) values computed by Jhanwar, Meath, and MacDonald [Can. J. Phys. 59 (1981) 185] shows that the techniques utilized in constructing the DOSDs provide a reasonably satisfactory estimate of the absolute photoabsorption oscillator strengths for the linear alkanes.