Accurate ground-state potential energy surfaces of the C₂H₂–Kr and C₂H₂–Xe van der Waals complexes

Abstract

Accurate ab initio intermolecular potential energy surfaces (IPES) have been obtained for the first time for the ground electronic state of the C₂H₂–Kr and C₂H₂–Xe van der Waals complexes. Extensive tests, including complete basis set and all-electron scalar relativistic results, support their calculation at the CCSD(T) level of theory, using small-core relativistic pseudopotentials for the rare-gas atoms and aug-cc-pVQZ basis sets extended with a set of 3s3p2d1f1g mid-bond functions. All results are corrected for the basis set superposition error. The importance of the scalar relativistic and rare-gas outer-core (n–1)d correlation effects is investigated. The calculated IPES, adjusted to analytical functions, are characterized by global minima corresponding to skew T-shaped geometries, in which the Jacobi vector positioning the rare-gas atom with respect to the center of mass of the C₂H₂ moiety corresponds to distances of 4.064 and 4.229 Å, and angles of 65.22° and 68.67° for C₂H₂–Kr and C₂H₂–Xe, respectively. The interaction energy of both complexes is estimated to be −151.88 (1.817 kJ mol⁻¹) and −182.76 cm⁻¹ (2.186 kJ mol⁻¹), respectively. The evolution of the topology of the IPES as a function of the rare-gas atom, from He to Xe, is also discussed.

Keywords:

• van der Waals complex
• ab initio
• acetylene
• rare gas
• potential energy surface

Acknowledgements

The authors thank Dr. L. Coudert (LISA, Paris) for helpful discussions and G. Destree from the ULB/VUB computer center for computational help. This work was sponsored by the Fonds National de la Recherche Scientifique de Belgique (FNRS, contract IISN) and the “Action de Recherches Concertées” de la Communauté française de Belgique.