An ab initio potential energy surface for the C_2H_2–N_2 system

摘要

An ab initio potential energy surface determined at the CCSD(T) level of theory is presented for the van der Waals complex C_2H_2–N_2. Additional calculations performed with the HF- and DFT- SAPT methods compare well with the CCSD(T) results and allow a better understanding of the main features of this interaction potential surface. An expansion of this surface over spherical harmonics has also been performed. The global energy minimum of the complex is obtained for the linear conformation. The T conformations are the least attractive. Such characteristics mainly arise because of the variation, in sign and in absolute value of the electrostatic energy between all these conformations. The specific role of the quadrupole–quadrupole interaction which involves two moments of opposite signs is therefore examined. The main features derived from the present surface are compared and discussed according to the following relevant systems: N_2–H_2,C_2H_2–H_2,C_2H_2–C_2H_2 and N_2–N_2. Calculated rotational constants for selected conformations of the C_2H_2–N_2 dimer are found to be in good agreement with available values.