High-resolution Doppler-free two-photon spectroscopic studies of molecules. I. Theν3bands ofCH312F

We report the first detailed studies of high-resolution Doppler-free two-photon absorption in molecular systems. The ${\nu }_3$ vibrational bands in ${}_{}{}^{12}{}_{}{}^{}\mathrm{CH}_3^{}{}_{}{}^{}$F are studied using two fixed-frequency infrared optical fields in combination with molecular Stark tuning. These measurements are used to formulate definite conclusions concerning the free-system properties and collisional interactions in the ${\nu }_3$ vibrational manifold. Specifically, the near coincidences of the $P14\mathrm{}$ and $P30\mathrm{}$ lines of two oppositely directed cw ${\mathrm{CO}}_2$ lasers at 9.6 μm with the $R{\mathrm{}(1,1)\mathrm{}}_{0\to {\nu }_3}$ and the $R{\mathrm{}(2,1)\mathrm{}}_{{\nu }_3\to 2{\nu }_3}$ lines in ${}_{}{}^{12}{}_{}{}^{}\mathrm{CH}_2^{}{}_{}{}^{}$F are used to determine the following properties: (1) precise transition energies for the $({\nu }_3,J,K)=(0,1,1)\mathrm{}\to \mathrm{}(2,3,1)\mathrm{}$ two-photon transition, (2) pressure-broadening coefficients, and (3) pressure-shift parameters. Finally, the influence of polarization on the properties of the two-photon signal amplitude is examined.