NEAR-INFRARED FOURIER-TRANSFORM RAMAN-SPECTRA OF PROTONATED AND DEUTERATED TRANS-AZOBENZENE ISOTOPOMERS

Near-infrared Fourier transform (NIR FT) Raman spectra of five irans-a zobenzene isotopomers and their protonated and deuterated forms were r ecorded. Trifluoroacetic acid was found to be a good protonation agent for measuring Raman spectra of protonated azobenzene. An assignment o f the most relevant vibrational modes (N=N stretching and N-H/N-H-2 in -plane bending) of the protonated and deuterated species is proposed. The N=N stretching band in irans-azobenzene isotopomers decreases by a bout 40 cm(-1) upon protonation, while it varies within +/- 10 cm(-1) upon deuteration with respect to the unprotonated (undeuterated) form. A comparison is made with the protonated form of the isoelectronic tr ans-N-benzylideneaniline. (C) 1997 Elsevier Science B.V.