Attacking a Small Beast: Ar–CO, a Prototype for Intermolecular Forces

Abstract

Abstract The study of intermolecular forces has been of increasing interest in the past. New theoretical and experimental techniques have been developed which allow an improved understanding of these important interactions. We will give an introduction to the theoretical concepts of the description of intermolecular forces. We will tackle Ar–CO as prototype system of intermolecular forces which has been subject of intensive experimental and theoretical work in the past and has evolved to one of the most investigated intermolecular complexes. We will give here an overview over the numerous theoretical and experimental studies which have been published in the literature. A comparison between the most recent ab initio studies and the experimental work demonstrates a lack of sufficient agreement. We have carried out a semi-empirical fit of the potential energy surface to five of the seven known intermolecular modes. All modes could be reproduced within 0.4 cm using our new potential energy surface. The most significant deviation which was found in comparison to previous ab initio potentials was the appearance of a second local minimum in the potential energy surface. These results indicate a lack of a sufficient accurate theoretical description of intermolecular forces for this “little beast” which remains still a challenge for the future.