The vacuum UV photoabsorption spectroscopy of the geminal ethylene difluoride (1,1-C2H2F2). The vibrational structure and its analysis

Abstract

The vacuum UV photoabsorption spectrum of 1,1-C 2 H 2 F 2 has been examined in detail between 6 eV and 25 eV photon energy by using synchrotron radiation. The broad band observed at 7.52 eV includes the π → π* and the 2b 1 → 3s Rydberg transitions. An analysis is proposed and applied to the fine structure belonging to these transitions. For the π(2b 1 ) → π* transition, one long vibrational progression is observed with ω 2 = 1475 ± 80cm 1 combined with one quantum of vibration of ω 4 = 976 ± 24cm 1 and its adiabatic excitation energy is determined at 6.742 eV. The 2b 1 → 3s Rydberg transition is characterized by a single progression with ω 2 = 1532 ± 80cm 1 starting at 6.957 eV. These vibrations are ascribed to the C=C and C-F stretching motions respectively. The abundant structure observed between 8.2 eV and 11.2 eV has been analyzed in terms of vibronic transitions to ns (δ = 0.98) and two different np (δ = 0.50 and 0.31) and nd (δ = 0.13 and 0.044) Rydberg series all converging to the 1,1-C 2 H 2 F 2 + (X 2 B 1 ) ionic ground state. An analysis of the associated vibrational structure of the individual Rydberg states has been attempted providing average values of the wavenumbers ω 2 = 1549 ± 16 cm 1 , ω 4 = 839 ± 40 cm 1 and ω 5 = 589 ± 16 cm 1 . Eight other Rydberg states were also analyzed. The vacuum UV spectrum of 1,1-C 2 H 2 F 2 has been recorded for the first time above 11.2 eV and up to 25 eV. Several broad and strong bands are tentatively assigned to transitions to Rydberg states which are members of Rydberg series converging to excited ionic states of 1,1-C 2 H 2 F 2 . For several of these Rydberg states vibrational structures are observed and assignments are proposed.

Vibronic valence and Rydberg transitions in geminal chloro-fluoro-ethene (1,1-C2H2FCl): a spectroscopic and quantum chemical investigation

“…In contrast with our observations in the 1,1-C 2 H 2 F 2 VUV-PAS [5], Figure 1 clearly shows a regular fine structure spread over the whole photon energy range investigated in this work. …”

“…However, the substitution of an F atom by a Cl atom seems to be crucial. This trend is confirmed by comparing the same spectral region in C 2 H 3 Cl [2] and C 2 H 3 Br [3], as performed in [5]. Owing to the weakness and the diffuseness of the structures in the 7.01-eV band displayed in Figure 5(a), the subtraction method described in Section 2.2 has been applied to disentangle its vibrational structure.…”

“…Comparing these three compounds, the peak maximum observed in the PAS of 1,1-C 2 H 2 FCl obviously shows a significant red shift of about 0.5 eV On the other hand the position of this maximum does not change significantly when the H atoms are substituted by one [1] or two F atoms [5]. However, the substitution of an F atom by a Cl atom seems to be crucial.…”

“…Later, its application has been extended to e.g. photoionization mass spectrometry [14], photoelectron [15] and photoabsorption [5] spectroscopy. Briefly, for this purpose, the experimental curve is strongly smoothed to simulate the underlying continuum which is then subtracted from the original spectrum.…”

“…on C 2 H 3 F [1], C 2 H 3 Cl [2] and C 2 H 3 Br [3], but also on C 2 H 2 FCl (1,1-and 1,2-isomers) [4], and more recently on 1,1-C 2 H 2 F 2 [5] using vacuum ultraviolet (VUV) photoabsorption and photoelectron spectroscopies. The ionization and dissociation dynamics were investigated by photoionization mass spectrometry and photoelectron-photoion coincidence spectroscopy.…”