FT-IR spectrum of the 2H-tautomer of benzotriazole in a supersonic jet

The infrared absorption spectrum of benzotriazole and N-deuterobenzotriazole in a cooled molecular beam have been measured and compared to those in the solid state. Small but significant differences in the spectra have been noted and attributed to the occurrence of primarily the 2H-tautomer in the beam and the 1H-tautomer in the solid. Optimized geometries and vibrational frequencies have been determined from ab initio molecular orbital and density functional calculations. Neither the molecular orbital calculations nor the spectra support a more quinonoid structure for the 2H-tautomer.