Stark Effect of F1(2) Line of Methane at 3.39 µm Observed by the Method of Inverted Lamb Dip

The small Stark effect of the F 1 (2) line of methane at 3.39 µm is studied. The observed Stark pattern does not reveal resolved Stark components at the maximum applied field intensity of 40 kV/cm. But it shows a broadening of particular asymmetry and it is in satisfactory agreement with the theoretical pattern of the second-order Stark shift as given by Δ ν=5.31×10 -2 M 2 E 2 kHz where M is the quantum number for the component of angular momentum along the Stark field and E is the magnitude of Stark field in kV/cm. Thus the Stark shift of this line in a weak field is extremely small so that a high accuracy as a frequency standard can be guaranteed.