https://doi.org/10.1351/goldbook.08232
Loss of coherence between the upper and lower states of a transition.
Notes:
- The term 'dephasing' arises from the density matrix formalism that is used in a phenomenological approach to simplify the description of the relaxation dynamics of a molecule coupled to its surroundings.
- Dephasing leads to either homogeneous broadening or inhomogeneous broadening depending on the system. The continually changing intermolecular interactions cause a shift of the frequency of the intramolecular vibration. If these interactions change much more slowly than the amplitude of this shift, heterogeneous broadening results and causes a Gaussian band. If these interactions change much faster than the amplitude of this shift, homogeneous broadening occurs and the observed spectral band is a notionally narrowed Lorentzian band. In the general case, the broadening due to dephasing is neither homogeneous nor heterogeneous and the line shape is neither Gaussian nor Lorentzian.