An ab initio electronic density study of the CH₄–Ar, CH₄–Xe, CH₄–H₂O and CH₄–H₂S complexes: insights into the nature of the intermolecular interaction

Abstract

The main point of this paper concerns the theoretical characterisation of the effects induced by the intermolecular interaction on the electron density upon the formation of CH₄-H₂X (X=O,S) and CH₄–Ng (Ng=Ar,Xe) complexes. The work has been stimulated by recent molecular scattering beams experiments, which point out differences in both strength and anisotropy of the intermolecular potential between CH₄–H₂X respect to reference CH₄–Ng systems. Herein, attention is focused on the electronic charge polarisation and particularly charge transfer (CT) effects between involved partners, directly related to the topology of the full potential energy surface. The modification of electron density and the occurrence of CT have been evaluated via the charge displacement function worked out by high level ab initio calculations. Moreover, in the case of a specific configuration of CH₄–H₂O system, we define the leading interaction components, including their relative stabilising role and test our intermolecular potential model with reference to ab initio calculations. The results obtained indicate that CT clearly affects the strength and the anisotropy of CH₄–H₂O complex, and covers a minor and negligible role for CH₄–H₂S and the noble gas complexes, respectively.

Keywords:

• Scattering experiments
• non covalent intermolecular interactions
• ab initio calculations
• charge transfer
• methane adducts

Additional information

Funding

This work was supported by the Italian Ministero dell’Istruzione, della Ricerca e dell’Università (PRIN 2010–2011) [Grant number 2010ERFKXL-002].