Gas-phase IR spectrum of 7-azaindole. Scaled quantum mechanical force field and complete spectrum assignment

Abstract

The gas-phase IR spectrum of 7-azaindole has been recorded from 100 to 4000 cm^–1, using a multipass cell heated to ca. 110 °C, and completely assigned using theoretical predictions based on the scaled quantum mechanical (SQM) method. The harmonic force field of 7-azaindole, evaluated at the HF-SCF level using 6-31G** orbitals, is corrected by scaling the force field over a convenient set of internal coordinates. Scaling factors were determined by least-squares fitting of the theoretical to the experimental frequencies of the two parent molecules, pyridine and pyrrole, and their perdeuteriated isotopomers. Our final prediction gives frequencies for 7-azaindole which on average differ from experiment by 18 cm^–1.