Saturation Spectroscopy of C2h4 Using a Co2-laser Side-band Spectrometer

We have studied the saturation spectrum of the nu(7) band of C2H4 using the tunable sideband CO2 laser technique coupled to a Fabry-Perot cavity containing C2H4. About 40 line frequencies have been determined with a typical 100-kHz accuracy. An overall fit including all available information on the coupled nu(4), nu(7), and nu(10) levels improves the nu(7) state and the ground state parameters. (C) 1995 Academic Press, Inc

Experimental determination of spin-rotation and spin-spin magnetic interactions in

When a gas sample of 13CH3F is prepared with a population of isomers (ortho and para forms) far from the equilibrium given by nuclear spin statistics, it relaxes towards this equilibrium with an exponential decay rate. This phenomenon called nuclear spin conversion is mainly governed by intramolecular spin-spin and spin-rotation interactions. In the quantum relaxation model [P.L. Chapovsky, Phys. Rev. A 43, 3624 (1991)], two pairs of ortho-para levels (J=9, K=3; J'=11, K'=1) and (J=20, K=3; J'=21, K'=1) are principally responsible for the conversion. The levels of the second pair are coupled by both spin-spin and spin-rotation interactions. The application of an electric field (up to 10 kV/cm) induces a crossing of the Stark components of this pair, which is observed for the first time. A specific experimental set-up based on an electric field of alternating triangular shape is used, which allows the determination of the strength of both interactions via the measurement of the spin conversion decay rates. This work yields the first experimental value for the electronic contribution to the spin-rotation interaction in 13CH3F

Saturation sideband CO2 laser spectroscopy of the overtone band 2 nu(2) and its hot band 3 nu(2)-nu(2) of carbonyl sulfide

The saturation spectra of the 2 nu(2) and the 3 nu(2)-nu(2) bands of carbonyl sulfide have been studied using a CO2 laser sideband spectrometer. The frequency of 20 absorption lines has been determined with an accuracy of 20 kHz. These data have been included in a global rovibrational analysis including all the other data available on (OCS)-O-16-C-12-S-32. We list an improved set of standard frequencies at the 10(-6) cm(-1) level. (C) 1998 Academic Press

Nuclear spin conversion in CH

The nuclear spin conversion in CH3F molecules subjected to an alternating electric field was investigated experimentally. The conversion rate was found to be almost unaffected by low electric fields ($\leq 200$ V/cm) but sharply increased tenfold when the electric field amplitude exceeds the values ($\simeq 800$ V/cm) sufficiently high to produce crossings of the ortho and para states of the molecule. A theoretical model for the molecular conversion in alternating electric field was developed. The results of the experiment were found to be in a good agreement with the theory