The splitting-up of degenerate electronic energy levels of linear molecules owing to interaction between the electronic states and the vibrational states. This vibronic interaction was analysed by Rudolf Renner in 1934, building on related work by Gerhard Herzberg and Edward Teller in 1933. The Renner effect was first observed in 1959 and has been extended to include the interaction between electronic states and rotational states. See also Jahn–Teller effect.