An ab initio potential energy surface for the C₂H₂–N₂ system

Abstract

An ab initio potential energy surface determined at the CCSD(T) level of theory is presented for the van der Waals complex C₂H₂–N₂. 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: N₂–H₂, C₂H₂–H₂, C₂H₂–C₂H₂ and N₂–N₂. Calculated rotational constants for selected conformations of the C₂H₂–N₂ dimer are found to be in good agreement with available values.

Keywords:

• ethyne
• acetylene
• nitrogen
• interaction potential
• potential energy surface

Acknowledgments

The authors thank Massimiliano Bartolomei (Instituto de Fisica Fundamental, CSIC, Madrid) for providing preliminary results obtained with the bond-bond methodology for the C₂H₂–C₂H₂ PES. FT acknowledges the financial support from the GDRI HiRESMIR (high resolution microwave, infrared and Raman molecular spectroscopy) for his participation in the Solvay workshop ‘Femto-, Astro-, Spectro-Ethyne’ held in Brussels in May 2012.

Notes

1. This expansion is available on request.