Resonant two-photon ionization spectroscopy of LiCu

Jet-cooled LiCu has been investigated using resonant two-photon ionization spectroscopy. A long vibrational progression was observed and identified as the [20.5] 1?+? X 1?+ band system. Ten bands of the system were rotationally resolved for 7Li63Cu, giving bond lengths of r0=2.2618(3) ? for the X 1?+ state and r'e=2.74(4) ? for the [20.5] 1?+ state. The fitted spectroscopic parameters of the [20.5] 1?+ state were used to obtain a RKR estimate of the [20.5] 1?+ potential energy curve. The unusual shape of this curve is thought to derive from avoided crossings between the Li1Cu2 ion pair state and covalent states, with the Li1Cu2 ion pair state ultimately correlating to the ground electronic state of the molecule.