The binding energies of the lowest energy complex containing a single Ar atom and a CH3ONO molecule are -3.73 kJ/mol for the cis conformer (2A), and -3.43 kJ/mol for the trans conformer (2B), see Table . This calculation again suggests that the difference in binding energies is -0.30 kJ/mol, where there is slight preference for the trans conformer compared to the cis conformer. Considering all optimized geometries of Ar:CH3ONO, the average binding energy of complexes involving the cis conformer is -2.37 kJ/mol and complexes involving the trans conformer is -2.79 kJ/mol, see Table . The difference in average binding energies of all stabilizing complexes is +0.12 kJ/mol. The lack of substantial preferential binding of Ar to trans-CH3ONO over cis-CH3ONO will be discussed in comparison with the experimental findings in Section 4.