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.