  The quantum physics of ions and electrons behind low-energy spectra of
strongly correlated {\it molecular} conductors, superconductors and Mott
insulators is poorly known, yet fascinating especially in orbitally degenerate
cases. The fulleride insulator Cs$_{3}$C$_{60}$ (A15), one such system,
exhibits infrared (IR) spectra with low temperature peak features and
splittings suggestive of static Jahn-Teller distortions with breakdown of
orbital symmetry in the molecular site. That is puzzling, for there is no
detectable static distortion, and because the features and splittings disappear
upon modest heating, which they should not. Taking advantage of the
Mott-induced collapse of electronic wavefunctions from lattice-extended to
nanoscale localized inside a caged molecular site, we show that unbroken spin
and orbital symmetry of the ion multiplets explains the IR spectrum without
adjustable parameters. This demonstrates the importance of a fully quantum
treatment of nuclear positions and orbital momenta in the Mott insulator sites,
dynamically but not statically distorted. The observed demise of these features
with temperature is explained by the thermal population of a multiplet term
whose nuclear positions are essentially undistorted, but whose energy is very
low-lying. That term is in facts a scaled-down orbital excitation analogous to
that of other Mott insulators, with the same spin $1/2$ as the ground state,
but with a larger orbital moment of two instead of one.
