A new global and compact analytical representation of the potential energy surface of triatomic systems: application to copper nitrosyl and water

Accurate ground state potential of Cu2 up to the dissociation limit by perturbation assisted double-resonant four-wave mixing

Perturbation facilitated double-resonant four-wave mixing is applied to access high-lying vibrational levels of the X ¹Σ_g ⁺ (0_g ⁺) ground state of Cu₂. Rotationally resolved transitions up to v^″ = 102 are measured. The highest observed level is at 98% of the dissociation energy. The range and accuracy of previous measurements are significantly extended. By applying the near dissociation equation developed by Le Roy [R. J. Le Roy, J. Quant. Spectrosc. Radiat. Transfer 186, 197 (2017)], a dissociation energy of D_e = 16 270(7) hc cm^-1 is determined, and an accurate potential energy function for the X ¹Σ_g ⁺ (0_g ⁺) ground state is obtained. Molecular constants are determined from the measured transitions and by solving the radial Schrödinger equation using this function and are compared with results from earlier measurements. In addition, benchmark multi-reference configuration interaction computations are performed using the Douglas-Kroll-Hess Hamiltonian and the appropriate basis of augmented valence quadruple ζ type. Coupled-cluster single, double, and perturbative triple calculations were performed for comparison.