Stark spectroscopy with the CO laser: The dipole moment of H2CO in the v2=2 state

Abstract

Some transitions of the 2ν₂←ν₂ hot band of H₂CO near 5.8 μm have been observed by the laser Stark technique using a 20 cm long intracavity absorption cell with about 4 mtorr total pressure at room temperature. The detection of this weak hot band (partial pressure in the v₂=1 state ?8×10⁻⁷ torr) illustrates the high sensitivity of intracavity laser absorption spectroscipy. From the measured resonant fields of the transitions, the dipole moment of H₂CO in the v₂=2 state has been determined. The use of phase sensitive detection at twice the Stark modulation frequency is illustrated; this 2f detection effectively measures the strength of the transient nutation signal in the absorbing gas, and in some cases results in a better signal to noise ratio than does conventional 1f detection.