Observation of the Stark effect in high-overtone band transitions of NH₃

A sensitive dye-laser spectrometer is constructed to observe the Stark effect of weak-overtone transitions in NH₃. A ΔP/P sensitivity of 10⁻⁶ is achieved with the help of a laser-noise-reduction system. A relatively short (30-cm) and narrow-gap (0.25-mm) Stark electrode makes it possible to apply a high electric field on molecular gas at low pressure (˜1 Torr). The Stark components of the v = 5 overtone band transitions of The rotational assignments are confirmed, and the dipole moment in the v = 5 excited vibrational state is determined to be 1.40 ± 0.02 D.