Absolute intensities of NH-stretching transitions in dimethylamine and pyrrole.

Vibrational spectra of vapor-phase dimethylamine (DMA) and pyrrole have been recorded in the 1000 to 13000 cm(-1) region using long path conventional spectroscopy techniques. We have focused on the absolute intensities of the NH-stretching fundamental and overtone transitions; Δν(NH) = 1-4 regions for DMA and the Δν(NH) = 1-3 regions for pyrrole. In the Δν(NH) = 1-3 regions for DMA, evidence of tunneling splitting associated with the NH-wagging mode is observed. For DMA, the fundamental NH-stretching transition intensity is weaker than the first NH-stretching overtone. Also, the fundamental NH-stretching transition in DMA is much weaker than the fundamental transition in pyrrole. We have used an anharmonic oscillator local mode model with ab initio calculated local mode parameters and dipole moment functions at the CCSD(T)/aug-cc-pVTZ level to calculate the NH-stretching intensities and explain this intensity anomaly in DMA.

Overtone spectra of 2-mercaptoethanol and 1,2-ethanedithiol.

Vibrational spectra of vapor-phase 1,2-ethanedithiol and 2-mercaptoethanol were recorded to investigate weak intramolecular interactions. The spectra were recorded with conventional absorption spectroscopy and laser photoacoustic spectroscopy in the 2000-11,000 cm(-1) region. The room temperature spectra of each molecule are complicated by contributions from several conformers. Anharmonic oscillator local-mode calculations of the OH- and SH-stretching transitions have been performed to facilitate assignment of the different conformers in the spectra. We observe evidence of hydrogen-bond-like interactions from OH to S, but not from SH to O or S. The OH to S intramolecular interaction in 2-mercaptoethanol is weak and comparable to that found in the OH to O interaction in ethylene glycol.

Vibrational overtone spectroscopy of three-membered rings.

We have recorded vapor-phase photoacoustic spectra of cyclopropane, ethylene oxide, and ethylene sulfide in the third, fourth, and fifth CH-stretching overtone regions. We have used a harmonically coupled anharmonic oscillator local mode model to facilitate analysis of the spectra. Fermi resonance between the CH-stretching and HCH-bending vibrations is essential to explain the observed wide and multistructured CH-stretching overtone bands. A number of weak combination bands can account for the remaining experimental features observed to the blue of the CH-stretching regions. We have reassigned the fundamental spectra of these three-membered rings.