Molecules that do not obey the Born-Oppenheimer approximation are difficult to deal with from either an experimental or a theoretical point of view. Most electronic structure calculations assume the Born-Oppenheimer approximation and produce adiabatic potential energy surfaces (PES). Treating molecules that do not, usually requires consideration of vibronic coupling between diabatic PESs. The spectra of such molecules are typically much more complex than corresponding molecules which are well described by the Born-Oppenheimer approximation. Their vibrational structure is often quite irregular and their rotational structure often departs markedly from that expected for simple rigid rotors.Fortunately much progress has been made in recent years both in the theoretical treatment of these molecules and the ability to obtain high quality vibrational and rotational spectra of these species which are typically chemically reactive and experimentally elusive. This talk will focus on comparing theoretical and experimental results for several specific molecules, which exhibit Jahn-Teller or pseudo Jahn-Teller effects and therefore do not obey the Bron-Oppenheimer approximation. These include methoxy, CH3O and CD3O, and its unsymmetrically substituted derivatives, CHnD3-nO and CHn(CH3)3-nO. Other examples include the nitrate radical, NO3, cyclopentadienyl, C5H5, and its unsymmetrically deuterated derivatives C5HnD5-n.

Reconciliation of spectroscopic results and electronic structure calculations for molecules that do not obey the Born-Oppenheimer approximation

248th National Meeting (2014)

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