INFRARED-ZERO-FREQUENCY DOUBLE RESONANCE IN A RESONANT D.C. STARK $FIELD^{\ast}$

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1984

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Ohio State University

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Two years $ago,^{a}$ we reported a study of the lineshapes of infrared laser radio frequency double resonance signals in $CH_{3}F$ that occur when the RF frequency goes to zero for the case when the infrared laser is in near resonance with a vibration-rotation transition. The $^{Q}Q(12,2)$ transition in $^{12}CH_{3}F$ and the $^{Q}R (4,3)$ transition in $^{13}CH_{3}F$ were studied. We showed that a theory in which the RF field is treated as a high-frequency Stark effect in the usual two-level system gave only rough qualitative agreement with experiment, and did not predict the changes in lineshape that occurred upon variation of the sample pressure and RF power. We attributed the poor agreement between theory and experiment to some sort of interaction between the many m components of the zero-field transition. We have now studied the infrared-zero-frequency double-resonance lineshape for the $^{Q}P(2,1)$ transition in $CH_{3}F$. A.D.C. Stark field applied to the sample cell in addition to the modulated $RF^{3}$ field brought the $M = 1\leftarrow 0$ transition into resonance with the $9P(22) CO_{2}$ laser. By adjusting the Rabi frequency for the laser interaction and the pressure broadening parameter, very good agreement between the observed and calculated lineshape has been obtained for this single M component. Although the pressure must be kept low because of the high Stark field, sufficient pressure variation has been obtained to allow estimation of the pressure broadening parameter for this transition.

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$^{\ast}$ This research was supported by the U.S. National Science Foundation. $^{a}$ A. Jacques and R. H. Schwendeman, Symposium on Molecular Spectroscopy, 1982.
Author Institution: Department of Chemistry, Michigan State University

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