THE $\nu_{2} + \nu_{4}$ BAND OF $^{12}CF_{4}$

Author Institution:From a high-resolution diode laser spectrum of cooled $^{12}CF_{4}$, line assignments in $\nu_{2}+\nu_{4}$ at $1066.4 cm^{-1}$ have been made for tetrahedral subspecies to J = 20, and in many cases to higher J, Spectroscopic constants have been obtained from a least-squares fit of the Hamiltonian, and the relative intensities of the assigned lines have been calculated. The ground- and excited-state rotational constants, Coriolis constant, and splitting of the $F_{1}$ and $F_{2}$: vibrational substates have the values \begin{eqnarray*} && B_{0} = 0.191688 \pm 0.000020 cm^{-1},\\ && B = 0.191442 \pm 0.000020 cm^{-1},\\ && C_{4} = - 0.3605 \pm 0.0002,\\ && \Delta = 0.5757 \pm 0.0017 cm^{-1}, \end{eqnarray*} The C-F bond length in the ground vibrational state is thus $r_{0} = 1.31752 \pm 0.00007$ {\AA}. The analysis of a combination band such as this provides a method of obtaining ground-state spectroscopic constants of spherical-top molecules directly from the infrared spectrum, without the necessity of measuring weak ``forbidden’’ transitions