Following the initial switch-on, the system is driven by the CW field until we reach the "steady-state" where the calculated probability flux at large R (here taken at R = 50 a.u.) is constant corresponding to 450 fs. At this time the internuclear distance in the excited state, Eq. ( ), is calculated for different values of the driving frequency and for different molecular densities. The results are shown in Fig. together with the corresponding linear transmission spectra. When the molecular slab is in vacuum, varies linearly with the pump frequency (black line in Fig. ) and is nearly independent of the molecular density. When the molecules are placed inside a resonant cavity, the dynamics drastically change demonstrating that the nuclear wavepacket is significantly slower near the polaritonic frequencies. Some indication regarding the origin of the observed phenomenon is shown in Fig. . Here we examine the CW dynamics of (panel (a)) at different driving frequencies. Once the CW drive is established, the system reaches the steady state regime and becomes a linear function of time meaning that the dissociation rate is constant. It is readily seen from Fig. that such a rate is frequency dependent. Next, we perform a linear regression of once the system reaches the steady state, and we evaluate the slope and the intercept as functions of the driving frequency (panel (b)). The slope (dashed black line) does not depend on the number density of molecules and varies approximately linearly with the frequency. The intercept, however, exhibits significant changes showing two well-resolved minima at polariton frequencies. In agreement with the results of Fig. this again illustrates that the slowdown of the dissociation process when the optical pumping is done at the polariton frequency is an early time phenomenon.