PRESSURE BROADENING PARAMETERS IN VIBRATION-ROTATION SPECTRA BY ANALYSIS OF LINESHAPES OF LASER-STARK TRANSITIONS

Abstract

$^{1}$M. R\""{o}mheld, private communicationAuthor Institution:At the lowest pressures (1-10 mtorr) the lineshapes of laser Stark transitions in molecules with predominantly first-order Stark effects are Gaussian functions of the applied electric field. The widths of such transitions depend on the Doppler width for the sample and the derivative of the frequency of the transition with respect to the Stark field. As the pressure is increased the transitions are pressure broadened and the lineshapes become Voigt profiles. We have used a minicomputer to control the electric field in a laser Stark spectrometer and to record the output of the spectrometer as a function of field. For a variety of transitions in $CH_{3} F$ and $CH_{3}CN$ at low pressure we have shown that the lineshape is well represented by a Gaussian function with the expected width. The relative intensities of transitions at different fields for a single laser line closely match the predicted values. The $J^{\prime}=2, K^{\prime}=1, M^{\prime}=1 \leftarrow J^{\prime\prime}=1, K^{\prime\prime}=1, M^{\prime\prime}=1$ transition in $CH_{3}CN$ is resonant with the p(20) line of the $N_{2} O$ laser at low enough Stark $field^{1}$ that the transition can be recorded at pressures up to 1 torr. Analysis of the Voigt profiles obtained at several pressures leads to a preliminary value of the pressure-broadened half-width at half height of 65 MHz/torr