Overtone intensities in neopentane and tetramethylsilane

The CH vibrational overtone transitions of vapour phase neopentane-d(0), -d (6), -d(9), and tetramethylsilane (TMS) are investigated via conventional a bsorbance spectroscopy and intracavity laser photoacoustic spectroscopy (IC L-PAS). The CH stretching overtones of neopentane-d(0) are observed in the energy range Deltav(CH) = 3-9 (8 400 to 22 000 cm(-1)) and in the range Del tav(CH) = 3-8 for the remaining neopentanes and TMS. While we have extended the range of previous studies, our main focus in this work has been on ove rtone intensities. The oscillator strengths of the neopentane-d(0) overtone transitions are determined directly by conventional absorbance spectroscop y for Deltav(CH) = 3-6 and via ICL-PAS with methane as an internal standard for Deltav(CH) = 4-7. The correspondence of measured intensities for the t wo techniques demonstrates the usefulness of the latter for higher overtone ICL-PAS spectra. The experimentally determined Morse parameters omega and omegax as well as the harmonically coupled anharmonic oscillator (HCAO) mod el are used in conjunction with dipole moment functions that are derived fr om ab initio computations to calculate overtone transition intensities for the neopentanes and TMS.