A deeper look into Herzberg-Teller vibronic coupling effect and spectroscopic signature of non-Condon systems

A physical explanation with rigorous basis for the newly emerging vibrational progressions due Herzberg-Teller vibronic coupling that show up in absorption spectra and quantum beats in photon echo signals, respectively, in linearly coupled non-Condon systems besides those arising under the Condon regime, thereby leading to further broadening of the make-up of the phonon-side-band, is provided. The spectroscopic signature of non-Condon systems, whose electronic transition dipole moment depends on nuclear coordinates exponentially, with linear electron-phonon coupling seems to increase the Condon intensity or both increase the Condon intensity and give rise to new bands with different intensity of linear and nonlinear absorption spectra. Model system calculations of a single-site (homogeneous)linear absorption spectra and pump-probe signals are provided.