High-resolution Stark spectroscopy of molecules by infrared and far-infrared masers

Some of the He-Ne and He-Xe laser lines in the infrared can be tuned within several gigahertz by applying an axial magnetic field. Stark patterns of vibration-rotation lines of organic molecules were observed at 3.36-, 3.39-, 3.50-, and 5.57-μm wavelengths. With applied Stark fields up to 50 kV/cm, many Stark components were resolved and some of the transitions of H
2
CO, HDCO, and CH
4
were definitely assigned. Molecular masers in the far infrared cannot be tuned over any appreciable range, but the Stark effects of the rotation lines of NH
3
at two fixed far-infrared frequencies of the D
2
O maser were observed. The observations of a Stark component of the
J = 3 \leftarrow 2
line at 171.6 μm and the forbidden Stark components of the
J = 6 \leftarrow 5
line at 84.1 μm are reported.