Fig. 3. Separation of nuclear and electronic contributions.

Calculated fractional difference signals for the molecule CHD, assuming 100% excitation. a The nuclear contribution, $\mathrm{\Delta }{S}^{\mathrm{nucl}}\left(q,{\mathbf{R}}^{+}\right)$, associated with the change in molecular geometry, ${\mathbf{R}}_0\to {\mathbf{R}}^{+}$, upon excitation (in black) and the small difference due to electronic effects, $\mathrm{\Delta }\mathrm{\Delta }{S}_{3\mathrm{p}}^{\mathrm{elec}}\left(q,\mathbf{R}\right)=\mathrm{\Delta }{S}_{3\mathrm{p}}^{\mathrm{elec}}\left(q,{\mathbf{R}}^{+}\right)-\mathrm{\Delta }{S}_{3\mathrm{p}}^{\mathrm{elec}}\left(q,{\mathbf{R}}_0\right)$ shown at ×10 magnification (in blue). The insert shows an overlap of the molecule in the excited state 3p geometry (R⁺, gray) and the ground-state equilibrium geometry (R₀, dark green). b The electronic contribution for the 3p state, $\mathrm{\Delta }{S}_{3\mathrm{p}}^{\mathrm{elec}}\left(q,{\mathbf{R}}^{+}\right)$, and for the molecular positive ion, $\mathrm{\Delta }{S}_{{\mathrm{CHD}}^{+}}^{\mathrm{elec}}\left(q,{\mathbf{R}}^{+}\right)$. Note that only the result for the 3p_x state is shown since the 3p_x and 3p_y states have nearly identical signals.