ENERGETICS OF BENZENE-AMMONIA DIMERS

Applying the 2CR2PI method we have obtained novel information about th e spectral structures of the heterodimers C6H6 . NH3 and C6H6 . ND3 ne ar the S-1 state of benzene. For the first time the ionization thresho ld and the dissociation energy of the heterodimers have been determine d. Preliminary results of ab initio calculations reveal that one of th e two suggested isomers is characterized by hydrogen-bonded configurat ions with hindered rotation of ammonia about its C-3 axis. The calcula ted dissociation energy D-0 of this isomer very well agrees with the v alue of (620 +/- 100) cm(-1) determined experimentally. Exciting the h eteroclusters to energy levels near the S-2 state of benzene no 2CR2PI signals were obtained due to fast internal conversion.