Far-Ultraviolet Spectra of Fluoroethylenes

Abstract

The vacuum ultraviolet spectra of the complete series of fluoroethylenes were measured from 2000 to 1150 Å under moderate resolution. The π*←π transitions are easily identified in all the spectra. In most cases their maxima are only slightly displaced from their position in ethylene, but a very large hypsochromic shift is found in going from the tri- to the tetrasubstituted derivative. Three Rydberg series are observed in all the spectra, converging to the π ionization potential. They all exhibit vibrational fine structure dominated by C=C stretching and twisting vibrations. In the highly fluorine substituted ethylenes the first Rydberg band is well separated from the π*←π band (at about 1900 Å) as in the highly alkyl substituted derivatives. There is no evidence for transitions of σ electrons in this part of the spectrum except perhaps at the high frequency end of the range (1200 Å).

The vacuum UV photoabsorption spectroscopy of vinyl fluoride (C2H3F): The vibrational fine structure and its analysis

“…Concerning the relative intensities in the low-energy part of the C 2 H 3 F PAS the best agreement is found with the PAS as reported by Bélanger and Sandorfy [19]. The intensity ratio R' between the 7.6 eV band and the 9.0 eV band is about 1.5 in the present work and R' = 2 in the PAS reported in Ref.…”

“…Similarly to C 2 H 4 [39] the PAS of C 2 H 3 F shows a first strong and broad band centered on a maximum at 7.6 eV (61 300 cm -1 or 163.1 nm) in good agreement with the earlier determination of Bélanger and Sandorfy [19] at 166.5 nm (7.45 eV or 60 060 cm -1 ) and of Sze et al [20] at about 7.5 eV (60 570 cm -1 or 165.1 nm). This band is unanimously assigned to the 2a" → π * (also called π → π * ) transition.…”

“…The intensity ratio R' between the 7.6 eV band and the 9.0 eV band is about 1.5 in the present work and R' = 2 in the PAS reported in Ref. [19]. Also in the present case a large discrepancy has to be mentioned with the VSEELS technique [20] which leads to R' ≈ 4.…”

“…Such broad bands are mostly assigned to valence-to-valence (V-V) transitions [19,20]. To support the interpretation, the vertical ionization energies of the successive valence orbitals of C 2 H 3 F as measured by HeI-PES [36] have been displayed in an energy level diagram (Fig.…”

“…The vacuum UV spectroscopic data reported on vinyl fluoride are very scarce. To the best of our knowledge the latest detailed work devoted to this molecule has been reported by Bélanger and Sandorfy [19]. These authors analyzed the vacuum UV spectrum of the six fluoroethylenes in the 50 000-82 000 cm -1 (6.2-10.2 eV) spectral region using a 1 m normal incidence (1 m-NIM) monochromator equipped with a 1200 l/mm grating.…”