# SUB-DOPPLER LASER-STARK MEASUREMENTS OF HYPERFINE STRUCTURE IN EXCITED VIBRATIONAL STATES OF $NH_{3}$

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 Title: SUB-DOPPLER LASER-STARK MEASUREMENTS OF HYPERFINE STRUCTURE IN EXCITED VIBRATIONAL STATES OF $NH_{3}$ Creators: Weber, W. H. Issue Date: 1985 Publisher: Ohio State University Abstract: Laser-Stark spectra showing well resolved hyperfine structure on 13 transitions in the $\nu_{4}$ and 2 $\nu_{2}$ bands of $^{14}NH_{3}$ are obtained and analyzed. Direct least-squares fits of the spectra yield determinations of the nuclear quadrupole coupling constant eqQ in the various states, accurate to about $\pm 1%$ (40 kHz) in favorable cases. To this accuracy, eqQ is the same in the ground and $\nu_{4}$ states, but it shows sizable changes in the $2\nu_{2}$ state, in agreement with the predictions of Spirko. The data are obtained using a CO laser and two precision Stark cells. One cell, placed inside the laser cavity, is used to Lamb-dip stabilize the laser on an $NH_{3}$ transition Stark-tuned into resonance with it. The other cell, placed in an external cavity, is used to record the data. Spectra of isolated lines, fit to a Lorentzian lineshape, show widths of 600 kHz (FWHM), a factor of 250 below the Doppler width. The key parameters needed to obtain such linewidths are the laser frequency stability, which is found to be $\pm 10$ kHz for periods of an hour or more, and the homogeneity of the Stark field, which is demonstrated through an analysis of broadening mechanisms to be $\pm 1.7 \times 10^{-4}$. Description: Author Institution: Physics Department, Research Staff, Ford Motor Company URI: http://hdl.handle.net/1811/12167 Other Identifiers: 1985-RF-1