Density functional studies of the pseudo-pi.A sigma charge-transfer complex between cyclopropane and chlorine monofluoride

The pseudo-pi.a sigma charge-transfer complex formed by cyclopropane and ch lorine monofluoride was studied with various approximate pure and hybrid de nsity functional methods and the second-order Moller-Plesset (MP2) theory. The calculations demonstrate that one hybrid method, namely the so-called B 3LYP, leads to reasonably good estimates of the experimentally measured rot ational constants. In addition, the predicted B3LYP intermolecular distance is found also to be close to the experimental value. This lends confidence to the prediction of the intermolecular interaction energy, which is found to be 1.42 kcal mol(-1). It was also possible to calculate the number and energies of the vibrational states supported by the intermolecular stretchi ng mode. Only five such states have been found. The performances of the var ious approximate density functionals and MP2 theory are compared and discus sed. Finally, the analysis of the natural bond orbitals, which has been fou nd to be very valuable in understanding the nature of the weak intermolecul ar interaction is discussed.