PURE ROTATIONAL SPECTRUM OF $CF_{4}$ IN THE $V_{3} = 1$ STATE OBSERVED BY INFRAFRED-RADIOFREQUNCY DOUBLE RESONANCE
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Date
1980
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Ohio State University
Abstract
Pure rotational transitions of $CF_{4}$ in the $\nu_{3}$ state were observed by ir-radiofrequency double resonance using a tunable diode laser (TDL) in Institute for Molecular Science. The laser beam was focused into a 30 cm long coaxial cell which was filled with about 1 MTorr of $CF_{4}$. The signal was observed as an increase of infrared absorption caused by saturating the pure rotational transitions among the $\nu_{3}$ tetrahedral splittings. Linewidth of the observed transition was 100 to 200 KHz in HWHM. Advantage of using a tunable laser in double resonance was well demonstrated by observing 176 pure rotational lines in the excited state, 40 in the $J_{J+1}, 116$ in the $J_{J}$ and 20 in the $J_{J-1}$ state. The observed spectrum was analyzed by directly diagonalizing the effective Hamiltonian by Robiette et al.. The analysis showed that the $J_{J-1}$ state was perturbed by the $2\nu_{4}$ state. From the observed lines in the $J_{J+1}$ and $J_{J}$ states, accurate molecular constants of the excited state were determined. The infrared Q-branch, where more than 2000 absorption lines were heavily overlapped within $0.8 cm^{-1}$, could also be analized simultaneously. Once a double resonance signal in the $J_{J}$ state was observed, the ir absorption and the double resonance signals were recorded simulataneously by scanning the TDL while the rf source was fixed at the resonance frequency. By this method, accurate wavelengths of more than 200 Q-branch lines could be measured.
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