The vibronic wavefunctions of the ⁴T₂, relaxed excited state of Cr³⁺ in α‐Al2O3 are determined when there are a Jahn‐Teller coupling with the E_g ‐mode and a trigonal potential which cannot be treated as a perturbation with respect to the electron‐vibration interaction. The interaction Hamiltonian with a uniaxial stress, parallel or perpendicular to the C₃,‐axis, is obtained. The experimental results are interpreted by the existence of a Jahn‐Teller effect with the E_g‐mode. Choosing 200 cm⁻¹ for the vibrational quantum energy, the Jahn‐Teller energy is calculated from the experimental data.