Fig. presents the real-space projected transition density (Eq. 13), where the photonic DOFs have been traced out, leaving only the electronic contributions mixed through the polaritonic expansion coefficients in the adiabatic matter/Fock basis (see Eq. 5). The theoretical details on computing the polaritonic transition density calculations are provided at the end of this letter. The lightmatter hybridization leads to super-positions between photon dressed electronic states. This results in changes of the transition density as a function of the coupling strength A 0 (varied along the X-axis of panel d) for the upper and lower polaritons, which correspond to the lowest-energy PESs, with a C-O bond length of 1.22 Å and at cavity energy ω c = 7.92 eV. Under this configuration, the cavity is nearly resonant with the molecular adiabatic transition from the ground state to the ψ A 1 1 state at the Frank-Condon point, according to the previous work in Ref. 31. Through mixing of the characters of electronic states, the transition density is modified for each coupling strength. The transition density obtained from the pQED simulation presented in panel d are visually identical to those obtained from scQED in Ref. 31.