Vibrational overtone spectroscopy, energy levels, and intensities of (CH3)3C-C≡C-H

The vibrational overtone spectra of the acetylenic (Δυ = 4, 5) and methyl (Δυ = 5, 6) C-H stretch transitions of tert-butyl acetylene [(CH(3))(3)C-C≡C-H] were obtained using the phase shift cavity ring down (PS-CRD) technique at 295 K. The C-H stretch fundamental and overtone absorptions of the acetylenic (Δυ = 2 and 3) and methyl (Δυ = 2-4) C-H bonds have been obtained using a Fourier transform infrared and near-infrared spectrophotometer. Harmonic frequency ω(ν(1)) and anharmonicities x(ν(1)) and x(ν(1), ν(24)) are reported for the acetylenic C-H bond. Molecular orbital calculations of geometry and vibrational frequencies were performed. A harmonically coupled anharmonic oscillator (HCAO) model was used to determine the overtone energy levels and assign the absorption bands to vibrational transitions of methyl C-H bonds. Band strength values were obtained experimentally and compared with intensities calculated in terms of the HCAO model where only the C-H modes are considered. No adjustable parameters were used to get order of magnitude agreement with experimental intensities for all pure local mode C-H transitions.