Advances in Molecular Relaxation and Interaction Processes, 20 (1981) 215-231 Elsevier Scientific Publishing Company, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONM Amsterdam -Printed in Belgium THE INTERMOLECULAR DIMER POTENTIAL OF NON-DIPOLAR LINEAR MOLECULES AHMED A. HASANEIN*, MAURO FERRARIO and MYRON EVANS Chemistry Department, University College of Wales, Aberystwyth. SY23 INE, Gt. Britain (Received 16 December 1980) ABSTRACT The intermolecular potentials of H2, D2, F2, 02, N2 and CO2 are examined using three independent estimates: i) The Kihara/Koide method, involving core anisotropy, van der Waals dispersion, quadrupolar interaction and octopolar induction terms. ii) The ab initio calculation for dimers of these molecules, using 4 - 31G and 6 - 31G basis sets. iii) The atom-atom (R.I.S.M.) method. While some consistent features emerge, there is qualitative disagree- ment in the majority of approach configurations which implies that the Kihara/Koide potential is overestimating the attractive part of the potential energy surface and underestimating the anisotropy of this surface in compari- son with the ab initio method. The atom-atom and Kihara/Koide potentials agree almost quantitatively in the majority of approach configurations, so that the extra electrostatic features considered by Kihara et al seem generally to have little effect on the atom-atom results. INTRODUCTION In the second of this series of papers' we aim to compare from different viewpoints some analytical potential forms for linear molecules. For non-dipolar polyatomic molecules, Kihara et al* have constructed an intermolecular potential function. u($- % [(fi/p)'a- a(%s] (1) * Permanent address: Chemistry Department, Faculty of Science, Alexandria University, Alexandria, Egypt 215 0378-4487/81/000~000/$02.50 0 1981 Elsevier Scientific Publishing Company