The n.a sigma charge-transfer complex formed by sulfur dioxide and chlorine monofluoride has been studied with various approximate pure and hybrid density functional methods and the second-order Moller-Plesset (MP2) theory. The calculations demonstrate that one pure method and one hybrid method, namely, the so-called BLYP and BHHLYP, respectively, lead to reasonably goad estimates of the experimentally measured rotational constants. However, the predicted BHHLYP intermolecular distance is found to be noticeably closer to the experimental value. Our best estimation for the intermolecular interaction energy is 1.93 kcal/mol. We have also been able to calculate the number and energies of the vibrational states supported by the intermolecular stretching mode. Only 11 such states have been found. The performance of the various approximate density functionals and the MP2 theory is compared and discussed. Finally, we comment on the analysis of the natural bond orbitals, which has been found to be very valuable to shed light on the nature of weak intermolecular interactions.