where θ is the standard deviation of the distribution. The complexity of evaluating these cross sections is that they require quantum dynamical propagation of vibrational wavepackets along multidimensional ground and electronic potential energy surfaces. To make further progress, it is useful to specialize considerations to the displaced harmonic oscillator model where the ground and excited state potential energy surfaces are described by N -dimensional harmonic surfaces with identical nuclear frequencies {ω α } and masses {m α } that are displaced in conformational space, with displacement d α along normal mode α. As shown by Shreve (Eqs. 15 and 17 in Ref. , for this model it is possible to analytically solve the quantum dynamics in Eq. ( ) and provide formulas for the cross sections that depend on the normal mode frequencies ω α , the Huang-Rhys factor S α = 1 2ℏ m α ω α d 2 α or reorganization energy λ α = ℏS α ω α , and the remaining spectroscopic parameters that define the cross sections. The total reorganization energy of the model is given by the sum of intramolecular and solvent reorganization energy λ = λ 0 + α λ α .