LEVEL CROSSING IN $^{13}CH_{3}F$ BY INFRARED-LASER STARK $SPECTROSCOPY^{\ast}$

$^{\ast}$This work was supported by the National Science Foundation. $^{1}$T. Amano and R.H. Schwendeman, J. Mol. Spectrosc. 78, 437-451 (1979).A zero-field level crossing involving the R(4,3) transition in the $\upsilon_{3}$ band of $^{13}CH_{3}F$ has been studied by means of infrared-laser Stark spectroscopy with a spectrometer operating with the electric field stepped under computer control. The level crossing spectra have been recorded for different infrared powers with a cell with 3 mm spacing and sample pressures ranging from 5 to 150 mtorr. The resonant frequency of the R(4,3) transition is 24.5 MHz less than the frequency of the 9P(32) $CO_{2}$ laser. The electric field of the radiation was set perpendicular to the Stark field. The level crossing in this transition is a superposition of level crossings involving the many m states. The experimental data have been analyzed by means of an algebraic solution to an expression for the change in absorption due to level crossing that was given previously in the form of a system of linear equations. Comparisons of observed and calculated lineshapes will be shown