Analysis of the intermolecular interaction between CH3OCH3, CF3OCH3, CF3OCF3, and CH4: High level ab initio calculations

Abstract

The intermolecular interaction energies of the CH3OCH3-CH4, CF3OCH3-CH4, and CF3OCF3-CH4 systems were calculated by ab initio molecular orbital method with the electron correlation correction at the second order Møller-Plesset perturbation (MP2) method. The interaction energies of 10 orientations of complexes were calculated for each system. The largest interaction energies calculated for the three systems are -1.06, -0.70, and -0.80 kcal/mol, respectively. The inclusion of electron correlation increases the attraction significantly. It gains the attraction -1.47, -1.19, and -1.27 kcal/mol, respectively. The dispersion interaction is found to be the major source of the attraction in these systems. In the CH3OCH3-CH4 system, the electrostatic interaction (-0.34 kcal/mol) increases the attraction substantially, while the electrostatic energies in the other systems are not large. Fluorine substitution of the ether decreases the electrostatic interaction, and therefore, decreases the attraction. In addition the orientation dependence of the interaction energy is decreased by the substitution.