Direct correlation method for OH, NH and CH local modes: vibrational overtone spectroscopy of biphenyl, anthracene, isobutanol, 2-chloroethanol and ethylenediamine at the third overtone region Original Research Article

The vibrational overtone spectra of gaseous biphenyl, anthracene, isobutanol, 2-chloroethanol and ethylenediamine at the Δv=4 vibrational overtone region have been recorded and assigned using the local mode model. For the spectral assignments, linear correlations were determined between the ab initio bond lengths (calculated in this work) and the overtone transition energies (taken from the literature) of aromatic and nonaromatic hydrocarbons, alcohols and amines. The bond lengths were obtained from ab initio geometry optimizations using both the 3-21G* and the 6-31G** basis sets. The bond length–overtone transition wavenumber correlations for the OH, NH and aromatic, methyl and methylenic CH oscillators are presented for the Δv=4 region for both basis sets. The bond lengths (CH for biphenyl and anthracene, OH for isobutanol and 2-chloroethanol and NH for ethylenediamine) were also determined. These bond lengths were used to predict the transition wavenumbers for Δv=4 transitions which could then be compared to the experimental values. These predictions which accounted for the possibility of various conformations agreed well with the experiment.