Born-Oppenheimer failure in the separation of low frequency vibrations

Mills, I. (1984) Born-Oppenheimer failure in the separation of low frequency vibrations. Journal of Physical Chemistry, 88 (3). pp. 532-536. doi: 10.1021/j150647a043

Abstract/Summary

Changes in the effective potential function of a low-frequency large-amplitude molecular vibration, resulting from excitation of a high-frequency vibration, are discussed. It is shown that in some situations a significant contribution to such changes may arise from failure of the Born-Oppenheimer separation of the low-frequency mode. In the particular example of the HF dimer, recent evidence that the tunneling barrier increases on exciting either of the H-stretching vibrations is probably due to this effect.