IR spectroscopy with FELIX .2. Lowest triplet state of azabenzenes

IR spectra of the lowest triplet state T-0 of pyrazine, pyrimidine and pyridine have been recorded by the use of the free-electron laser FELIX. Vibrational transitions have been observed as laser-induced changes in the intensity of the phosphorescence from T-0. Five triplet vibrations have been recognised for pyrimidine and two for pyridine. For pyrazine, all seven fundamental IR-active triplet vibrations in the range 250-2000 cm(-1) have been detected and the vibrational frequencies are found to be considerably lower than the corresponding ones in the ground state.