Systematic theoretical studies of the interaction of 1,4-diazabicyclo [2.2.2]octane (DABCO) with rare gases.

We investigate the intermolecular 1,4-diazabicyclo [2.2.2] octane (DABCO) interaction potential with He, Ne, Ar, and Kr rare gases (Rg) by means of post Hartree-Fock and the newly implemented explicitly correlated coupled cluster approaches in connection with several basis sets. After benchmarking computations, we show that the inclusion of diffuse atomic orbitals is mandatory for the accurate description of structures, energetics, and spectroscopic properties of DABCO-Rg van der Waals clusters and that the (R)MP2∕aug-cc-pVXZ (X = D, T) level is accurate enough for that purposes. For the neutral and ionic DABCO-Rg complexes, we characterized the low energy stationary points on the ground state potential. Most of the computed structures show a distortion along the low frequency mode of the van der Waals complex. Tunneling through this potential barrier leads to a splitting of the ground vibrational levels of several cm(-1). Our results served to reassign the available experimental spectra for DABCO(0,+1)-Ar and DABCO(0,+1)-Kr.