Structural, vibrational, and rovibrational analysis of tetrafluoroethylene

Abstract

High resolution FTIR spectra of (13)C enriched tetrafluoroethylene (C(2)F(4)) were measured at 150 K at the Australian Synchrotron. Rovibrational transitions were assigned in the a-type symmetric and b-type antisymmetric CF(2) stretches of (12)C(13)CF(4) and (13)C(2)F(4) near 1170 cm(-1) and 1300 cm(-1), respectively. Ground vibrational state spectroscopic constants for both molecules were determined in addition to the upper state constants for ν(11) and ν(9) of (13)C(2)F(4) and ν(11), ν(2)+ν(6), and ν(5) of (12)C(13)CF(4). The ground state constants, along with those determined for the (12)C(2)F(4) isotopologue from previously published data, were used to determine a semi-experimental r(e) structure r(CC) = 132.36 ± 0.37 pm, r(CF) = 131.11 ± 0.23 pm, α(FCC) = 123.3 ± 0.3° in excellent agreement with ab initio structures. Lower resolution FTIR spectra were measured between 100 and 5000 cm(-1) at room temperature and band centres obtained for all modes of the three isotopologues; although only 5 out of 12 modes in (12)C(2)F(4) and (13)C(2)F(4) are infrared (IR) active, the others were inferred from combination and hot-band positions. A number of modes are observed to be infrared active only in the (12)C(13)CF(4) isotopologue due to its lower symmetry. Most notably, decoupling of the antisymmetric CF(2) motions in the two halves of (12)C(13)CF(4) results in 2 strongly IR active modes that involve motion at one carbon or the other.

Vibrational Anharmonicities and Reactivity of Tetrafluoroethylene

“…23 The molecular force field at this level of theory was shown in the previous study to reproduce the fundamental wavenumbers and the isotopic shifts of C 2 F 4 very satisfactorily (for details, see ref (1)), and hence was an appropriate choice for computing x ij values. The calculations were performed for each of the 12 C 2 F 4 , 12 C 13 CF 4 , and 13 C 2 F 4 isotopologues.…”

“…1 For convenience Table 1 lists the fundamentals again. In this work we derived a large set of experimental anharmonic constants from combination bands and—in particular for the lower-wavenumber vibrations—from hot bands, and report a complete set of theoretically computed values.…”

“…21 The dimerization product C 2 F 4 was separated from CHClF 2 by low-temperature distillation. 1,21 …”

“…1 At the Synchrotron lab, the isotopically enriched sample was measured at moderate 0.1 cm –1 resolution in the far IR region from 100 to 600 cm –1 (capturing the band at 210 cm –1 ), and at high resolution for the IR active CF stretch bands, see ref (1). The present work focuses on anharmonic constants of 12 C 2 F 4 .…”

“…Only where the constants were expected to be different for 12 C 13 CF 4 and 13 C 2 F 4 (e.g., in the case of Fermi resonance) were the bands for these isotopologues evaluated to recover the corresponding constants. For the fundamentals and their isotopic shifts, see ref (1). …”