  Temperature-dependent reflectivity studies on the non-magnetic kagome metal
RbV$_3$Sb$_5$ in a broad energy range (50 cm$^{-1}$ $-$ 20000 cm$^{-1}$,
equivalent to 6 meV $-$ 2.5 eV) down to 10 K are reported. Below $T_{\rm
CDW}=102$ K, the optical spectra demonstrate a prominent spectral-weight
transfer from low to higher energies as the fingerprint of the charge-density
wave (CDW) formation with the opening of a partial gap. A detailed analysis
reveals two energy scales of, respectively, $\sim$ 800 cm$^{-1}$ (100 meV) and
360 cm$^{-1}$ (45 meV), the latter visible below 50 K only. Additionally, two
modes at, respectively, 160 cm$^{-1}$ (20 meV) and 430 cm$^{-1}$ (53 meV) can
be traced both above and below $T_{\rm CDW}$. They show strong anomalies
already above $T_{\rm CDW}$ with a further renormalization across the
transition, suggesting the importance of the electron-phonon coupling in
RbV$_3$Sb$_5$ in both normal and CDW states. While the 160 cm$^{-1}$ mode can
be attributed to the E$_{1u}$ phonon, the 430 cm$^{-1}$ mode could not be
reproduced in our phonon calculations. The antiresonance nature of this mode
suggests a nontrivial electron-phonon coupling in RbV$_3$Sb$_5$. A distinct
localization peak observed at all temperatures signals damped electron
dynamics, whereas the reduced Drude spectral weight manifests moderate
deviations from the band picture in RbV$_3$Sb$_5$.
