Fig. , presents the lowest bright excitation in formaldehyde when it is coupled to a cavity. In panel (i), when varying coupling strengths λ = 0.0, 0.02, 0.04, and 0.06 a.u., one can clearly see an an increasing Rabi splitting Ω R in the absorption spectra. The transition density of the bare molecular system is shown in panel (ii) right figure while the ground state density is shown in panel (ii), left figure. Inside the cavity, for a weak coupling (λ = 0.02 a.u.), the transition density from the ground state to the upper polariton (iii, right) and to the lower polariton state (iii, left) indicate a significant modification of the excitation character compared to the transition density for the bare molecule. Similarly, at increased coupling strength (λ = 0.06 a.u.). the transition density continues to change, although, the ground to the lower polariton transition (iv, left) is significantly modified compared to the case in (iii, left).