Ground-State Electric Dipole Moment of Methane

Linear Stark shifts and allowed electric dipole transitions have been observed for the first time in the ground electronic and vibrational state of a conventionally nonpolar molecule. By means of molecular-beam techniques, the electric dipole moment of CH₄ in its ground vibronic state has been determined to have a magnitude of (5.38 ±{} 0.10) ×{} 10^-6 D.