Potential energy function of CN-

The potential energy curve of the molecular negative ion CN- is constructed by morphing an accurate ab initio potential to available rotational data [C.A. Gottlieb, S. Brünken, M.C. McCarthy, P. Thaddeus, J. Chem. Phys. 126 (2007) 191101] within the framework of the reduced potential curve approach of Jenč [F. Jenč, Adv. Atom. Mol. Phys. 19 (1983) 265]. Using this potential energy curve, rotational spectroscopic constants are evaluated for the ground and firstly excited vibrational states of 12C15N−, 12C15N− and 13C14N−.