The small dipole moment of GeH4 induced by centrifugal distortion of the tetrahedral structure is measured by three experimental techniques using coincidences between the ν2 Q(11)E transition of GeH4 and infrared CO2 laser lines: (1) the Stark shift of the infrared-microwave double resonance, (2) infrared-infrared double resonance using modulation sidebands, and (3) laser Lamb-dip Stark spectroscopy. The observed results demonstrate the power of these methods in measuring small Stark shifts. From the observed shifts, Watson's centrifugal dipole moment has been determined to be θzxy=(3.33±0.05)×10-5 D for the ground vibrational state. For the excited state the Stark shift was found to be smaller than the ground state by a factor of 9, indicating approximate cancellation between rotation- and vibration-induced dipole moments for the rotational level in the ν2 vibrational state of GeH4.
Bibliographical noteErratum can be found in Physical Review A, 16(3), p. 1337, 1977.