CENTRIFUGAL DISTORTION ANALYSIS OF RARE GAS$\cdots$ROMATIC MOLECULE COMPLEXES

Author Institution: Department of Physics, Ohio State University; Labortorium fur Physikalische Chemie, Eidgen\""{o}ssische Technische HochschuleCentrifugal distortion constants obtained form microwave spectroscopy can be a valuable source of information regarding the van der Walls force field of complexes provided the amplitudes of the van der Walls modes are not too large. In complexes between a rare gas atom and a planar $C_{2}v$ monomer, the complete van der Waals force field is determinable form the quartic centrifugal distoration constants. In such complexes this amounts to 3 diagonal force constants and an off-diagonal bend-stretch force constant. The contribution made to the centrifugal distortion constants of the complex due to the vibrational modes of the monomer can be partially taken into account given the centrifugal distortion constants of the monomer. Using and assumed anharmonic potential function a pseudo structure can also be determined for the complex. If the ${x}$ axis is denoted as the axis perpendicular to the symmetry plane of the complex then the planar moment of inertia about this axis $(P_{x})$ should be equal to the planar moment of inertia about this same axis in the monomer $(P^{\prime}_{x})$. It can be shown that the difference ($\Delta P_{x}$) between these two planar moments of inertia is analogous of the inertia defect of planar molecule in that the anharmonic contribution to this quantity cancels exactly to first order. Hence a comparison between the calculated value of $\Delta P_{x}$ and the observed value gives and indication as to how well a harmonic model approximates the actual van der Walls vibrational motions. The above approach has been applied to the complexes pyrieine $\ldots Ar_{1}$ Pyrrole $\ldots$ furan $\ldots$ Ar and 1,1-difluoroethylene $\ldots Ar_{1}$ the results of which will be presented