parameter determined by reproducing experimental data. Alternatively, one can avoid explicit use of derivative couplings by switch from the adiabatic to the diabatic representation of the potential energy surfaces. Although rigorous validation of a diabatic representation requires knowledge of vibronic coupling, it is often possible to construct such diabatic representations by referencing the continuity of physical quantities such as dipole moment, charge distribution or orbital occupations. However, such construction requires detailed knowledge of a molecular system and introduces significant arbitrariness. Diabatic representations constructed with different method can yield different results and the reliability of the result relies on the discretion of the researcher. Theoretical development The first discussion of the effect of vibronic coupling on molecular spectra is given in the paper by Herzberg and Teller. Although the Herzberg–Teller effect appears to be the result of either vibronic coupling or the dependence of the electronic transition moment on the nuclear coordinates, it can be shown that these two apparently different causes of the Herzberg–Teller effect in a spectrum are two manifestations of the same phenomenon (see Section 14.1.9 of the book by Bunker and Jensen). Calculations of the lower excited levels of benzene by Sklar in 1937 (with the valence bond method) and later in 1938 by Goeppert-Mayer and Sklar (with the molecular orbital method) demonstrated a correspondence between the theoretical predictions and experimental results of the benzene spectrum. The benzene spectrum was the first qualitative computation of the efficiencies of various vibrations at inducing intensity absorption. See also Jahn–Teller effect Born–Huang approximation Born–Oppenheimer approximation Conical intersection References Quantum chemistry Molecular vibration Dynamics (mechanics)