A potential energy surface for the ground state of acetylene, H₂C₂([Xtilde]¹Σ_g⁺)

Abstract

A potential energy function has been derived for the ground state surface of C₂H₂ as a many-body expansion. The 2- and 3-body terms have been obtained by preliminary investigation of the ground state surfaces of CH₂([Xtilde] ³ B ₁) and C₂H([Xtilde] ²Σ⁺). A 4-body term has been derived which reproduces the energy, geometry and harmonic force field of C₂H₂. The potential has a secondary minimum corresponding to the vinylidene structure and the geometry and energy of this are in close agreement with predictions from ab initio calculations. The saddle point for the HCCH-H₂CC rearrangement is predicted to lie 2·530 eV above the acetylene minimum.