Spectroscopic characterization of the C2-Ne van der Waals complex

Binary complexes of C2 with rare-gas atoms (C2-Rg) have attracted theoretical interest as their potential-energy surfaces are predicted to support linear equilibrium geometries, without the local minimum for the T-shaped geometry that would be expected using a standard pair-potential model. In the present work we have explored the properties of C2-Ne using laser-induced fluorescence detection of the D 1Sigmau +-X 1Sigmag + transition. Bands of the complex were observed in association with the monomer 0-0 and 1-1 transitions. Rotationally resolved data yielded rotational constants of B'=0.099(3) cm(-1) and B"=0.100(3) cm(-1) for the excited and ground states, respectively. Analysis of the rovibrational energy-level structure for C2(D)-Ne indicates that the complex has a linear equilibrium structure with a barrier to internal rotation of approximately 15 cm(-1). Data for the ground state validate a recent high-level ab initio calculation of the potential-energy surface for C2(X)-Ne.