ABINITIO 2ND-ORDER AND 4TH-ORDER MOLLER-PLESSET STUDY ON STRUCTURE, STABILIZATION ENERGY, AND STRETCHING VIBRATION OF BENZENE...X (X=HE,NE,AR,KR,XE) VANDERWAALS MOLECULES

The C6v structure of benzene...X (X = He, Ne, Ar, Kr, Xe) complexes was investigated with second-order Moller-Plesset (MP2) theory; for the benzene ... He the whole potential-energy surface (PES) was also studied. The stabilization energy of the benzene ... He was also determined at the fourth-order Moller-Plesset (MP4) level; the respective MP4 stabilization energy is almost identical with MP2 stabilization energy which is due to the compensation of MP3 and MP4 contributions. The ab initio MP2 intermolecular distances agree nicely for all the complexes studied with the experimental value. While the stabilization energy of benzene...He and benzene...Ne (67 cm-1; 99 cm-1) is considerably smaller than that of benzene...Ar (429 cm-1), the intersystem distance differs less (3.32 angstrom, 3.50 angstrom, 3.53 angstrom). The stabilization energies and intersystem distances for benzene...Kr and benzene...Xe are 485 and 601 cm-1 and 3.71 and 3.89 angstrom, respectively. The PES of benzene...He differs from that of benzene...Ar and can be characterized as more isotropic. The harmonic and anharmonic stretching frequencies were determined for all the complexes; anharmonicity plays a crucial role only for the benzene...He complex. Theoretical and experimental stretching frequencies for benzene...Ar and benzene...Kr agree very well.