THE BENZENE-ARGON COMPLEX - A GROUND AND EXCITED-STATE AB-INITIO STUDY

Equilibrium dissociation energies D-e of the benzene-argon van der Waa ls complex are calculated in the ground state S-0 and in the excited s tate S-1 using integral-direct coupled cluster methods. The results co nfirm previous investigations of S-0, showing that high quality correl ation consistent basis sets and connected triple excitations are imper ative far a good description of the van der Waals complex. We estimate the CCSD(T) dissociation energy D-e= 389+/-2 cm(-1) for the ground st ate S-0. Using the CCSD linear response approach the frequency shift ( redshift) delta nu(e) =19 cm(-1) is obtained. Accurate spectroscopic s tructural data and frequency shifts delta nu(0) for the 6(0)(1) band o f the S-1<--S-0 transition are available for most of the benzene-rare gas atom complexes. However, the experimental determination of absolut e dissociation energies of these complexes is connected with much larg er uncertainties. The theoretical result agrees very well with the exp erimentally available redshift, showing that integral-direct coupled c luster methods will become an important tool in the study of van der W aals complexes in the future. (C) 1998 American Institute of Physics.