Overtone spectroscopy of 3,3,3-trifluoropropyne

Intracavity dye laser photoacoustic spectra have been obtained for overtone excitation of the C-H stretch (Δv₁ = 4, 5, and 6) of gas-phase CF₃O≡CH. Standard infrared techniques were used to obtain the fundamental and lower overtones (Δv₁ = 1, 2, 3). The local-mode model is used to assign prominent peaks. For all transitions in the C-H stretching mode a band close in energy to the main absorption is observed and is assigned as a hot band (v₁ = 0, v₇ = 1) → (v₁ = v, v₇ = 1) for v = 1-6, which shows the strong interaction between the C-H stretching mode (v₁) and the C-H bending mode (v₇). Also the fundamental and lower overtones (Δv₂ = 1, 2, 3) of the C≡C stretch are obtained. Harmonic frequencies (ω_i) and anharmonicity constants (X_ii) with i = 1 or 2 for C-H and C≡C bonds, respectively, are calculated. The off-diagonal local-mode - normal-mode anharmonicity constant X₁₇ derived from the interaction between modes v₁ and v₇ is also reported. Peak absorption cross sections are obtained for v₁ = 1-5 of CH absorptions and v₁ = 1-3 of C≡C absorptions.