Overtone spectroscopy of 3,3,3-trifluoropropyne

Abstract

Intracavity dye laser photoacoustic spectra have been obtained for overtone excitation of the C-H stretch (deltanu/sub 1/ = 4, 5, and 6) of gas-phase CF/sub 3/C(triple bond)CH. Standard infrared techniques were used to obtain the fundamental and lower overtones (deltanu/sub 1/ = 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 (nu/sub 1/ = 0, nu/sub 7/ = 1) ..-->.. (nu/sub 1/ = nu, nu/sub 7/ = 1) for nu = 1-6, which shows the strong interaction between the C-H stretching mode (nu/sub 1/) and the C-H bending model (nu/sub 7/). Also the fundamental and lower overtones (..delta..nu/sub 2/ = 1, 2, 3) of the C(triple bond)C stretch are obtained. Harmonic frequencies (omega/sub i/) and anharmonicity constants (X/sub ii/) with i = 1 or 2 for C-H and C(triple bond)C bonds, respectively, are calculated. The off-diagonal local-mode-normal-mode anharmonicity constant X/sub 17/ derived from the interaction between modes nu/sub 1/ and nu/sub 7/ is also reported. Peak absorption cross sections are obtained for nu/sub 1/ = 1-5 of CH absorptions and nu/submore » 1/ = 1-3 of C(triple bond)C absorptions.« less