THE MOLECULAR-STRUCTURE OF THE (NCCN)2 AND (PCCP)2 VAN-DER-WAALS DIMERS

The stationary points on the potential energy surfaces of the (NCCN)2 and (PCCP)2 van der Waals homodimers have been examined at the ab init io Hartree-Fock level of theory employing a 4-31G basis set. Only a T- shaped C2v stable minimum energy structure was found for the (NCCN)2 d imer, while two energetically very similar stable minima, exhibiting n ear T-shaped C(s) and slipped-parallel C2h spatial arrangements, were predicted for the (PCCP)2 dimer. Our predictions for the (NCCN)2 compl ex are in agreement with a recent gas phase spectroscopic study. No ex perimental gas phase study seems to have been reported for the (PCCP)2 dimer, and our results indicate that an equilibrium between a near T- shaped and a parallel form is likely to occur. The implications of inc luding electron correlation effects and higher polarized/diffuse funct ions are discussed.