Knowledge Bank

Dipole moments for the $(0,0,5)(15,552cm-1)$ and $(1,0,5)(17,550cm-1$) vibrational overtone levels of HCN have been determined: $\mu 005=3.141\pm 0.004D$ and $\mu 105=3.159\pm 0.011D$. The experiment uses an applied DC electric field, in which the Stark plates form two walls of a resonant acoustical cell. The apparatus is placed within the cavity of a narrowband, visible dye laser, and is rotated to measure both parallel and perpendicular DC Stark shifts. The photoacoustic signal is detected with a microphone attached to the ground plate. Observed ground state Stark shifts provide an internal calibration of the applied field. The experimental dipole moments will be compared to ab initio and semi-empirical predictions for the dipole moment function.