High-resolution infrared and laser photoacoustic spectroscopy of monochloroacetylene

Abstract

High-resolution vibration—rotation spectra of monochloroacetylene (HCCCl) have been recorded in two different wavenumber regions. Fourier transform infrared interferometer measurements in the 4000–10000cm−1 range have been performed with a resolution of 0.005–0.016cm−1 and titanium: sapphire ring laser intracavity photoacoustic measurements in the 12500–12600cm−1 and 12800–12860cm−1 regions have been carried out with a Doppler-limited resolution of about 0.02 cm−1. Altogether, 40 vibrational bands belonging to the HCC35 Cl and 15 bands belonging to the HCC37 Cl isotopic species have been rotationally assigned. A vibrational model, based on the conventional rectilinear normal coordinate theory including anharmonic Fermi, Darling—Dennison and vibrational l-type doubling resonances, has been used to attach vibrational labels to the bands. This approach is found to describe well the rovibrational energy level structure at least in the energy range covered in this work. The model shows that the CH oscillator becomes decoupled from the rest of the molecule as vibrational energy increases.