The 2(1)Pi(g) state of Rb-2 has been observed using the infrared infrared double resonance method. The low part of the potential curve of the state is characterized for the first time. The absolute vibrational numbers are determined with isotope effect. The molecular constants of this state are obtained from a Dunham fit and the potential curve of the state is constructed using the Rydberg-Klein-Rees method. (C) 2012 Elsevier B.V. All rights reserved.