The Jahn-Teller theorem (1937) states that any non-linear molecule with a degenerate electronic ground state will spontaneously distort to remove the degeneracy. For an E⊗e system (doubly degenerate state coupled to E-mode vibration), the potential surfaces form a Mexican hat: V±(Q) = ½ω²Q² ± F·Q, with the lower sheet having a minimum at Q = F/ω² called the Jahn-Teller stabilization energy E_JT = F²/(2ω²). Tunneling through the three equivalent minima (for cubic symmetry) creates a vibronic ground state with characteristic pseudo-rotational motion around the hat brim.