Stark Effect of the Absorption Line of Methane Observed by the 3.391 µm He-Ne Maser

The Stark effect in CH 4 which has no permanent dipole moment in the ground vibrational state is observed on one component line at 2947.802 cm -1 of the P (7) line in the ν 3 band by a magnetically tuned infrared maser. The effect is interpreted on the basis of the second-order induced dipole moment in the degenerate vibrational state which has the F 2 symmetry. The magnitude of the induced dipole moment of CH 4 in the ν 3 vibrational mode is evaluated from the observed Stark effect.