High-resolution spectroscopy of the 16-μm bending fundamental of CF4

The 16-μm bending fundamentals (ν₄) of ¹²CF₄, ¹³CF₄, and ¹⁴CF₄ have been observed at Doppler-limited resolution using a tunable PbSnSe semiconductor diode laser. The tetrahedral splittings of the rotational manifolds have been observed in all three branches, and in particular the dense and partially overlapping transitions in the Q branches have been resolved and assigned. A least-squares fit of the Hamiltonian, including off-diagonal terms, yielded five scalar and three tensor spectroscopic constants for each of the three isotopes. From these constants the upper-state rotational constant B₄ and the Coriolis constant ζ₄ have been calculated, together with some of the other molecular constants. An absorption feature at about 0.18 cm^?1 to the red of the main Q branch of each isotopic species has been identified as the Q branch of (ν₂ + ν₄) ? ν₂, which is the transition that lases when CF₄ is pumped by a CO₂ laser at 9.4 μm (i.e., in ν₂ + ν₄).