Intensities of CH-stretching overtones in 2-butenes

Abstract

The gas phase vibrational overtone spectra of trans-2-butene and cis-2-butene are recorded in the ΔνCH=1−6 regions by Fourier transform infrared and conventional near infrared-visible spectroscopy. Overtone spectra in the ΔνCH=5−9 regions are recorded by intracavity dye/titanium: sapphire laser photoacoustic spectroscopy. Absolute oscillator strengths are obtained from the conventional spectra. Oscillator strengths are calculated with a harmonically coupled anharmonic oscillator local mode model and ab initio dipole moment functions. The experimental and calculated oscillator strengths are compared. Spectral absorptions that are not due to transitions to pure local mode states or to local mode combination states, are observed in the spectra of both molecules, and are believed to be due to absorptions that involve methyl group torsion.