MULTIPHOTON IONIZATION SPECTROSCOPY OF DIFLUOROMETHYL RADICALS
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Date
1991
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Publisher
Ohio State University
Abstract
The structures and optical spectroscopy of the $CHF_{2}$ radical and cation were studied by initio molecular orbital calculations and by experiment. Ab initio calculations at the MP2/6-31G$^{**}$ theory level found that the optimum structure of the $\bar{X}$ $^{1}A_{1} CHF^{+}_{2}$ cation belongs to the $C_{2\nu}$, point group with $r(C-F) = 1.2424$ {\AA},$r(C-H) = 1.0883$ {\AA} and $\angle{F-C-F} = 119.19^{\circ}$.The optimized structure of the ground state $CHF_{2}(\bar{X}^{2}A^{\prime}$ radical belongs to the C point group with $r(C-F) = 1.3360$ {\AA}, $r(C-H) = 1.0883$ {\AA} $\angle{F-C-F} = 111.51^{\circ}$ and $\angle {H-C-F}=113.65^{\circ}$ The ab initio angle between the F-C-F plane and the C-H bond is $\Phi_{\pi} = 44.53^{\circ}$. Vibrational frequencies for each $CHF_{2}$ species were computed. The electronic spectra of $CHF_{2}$ and $CDF_{2}$ radicals were observed between 330-430 nm using mass resolved resonance enhanced multiphoton ionization (REMPI) spectroscopy. These spectra arose from two-photon resonances with planar Rydberg states. A third laser photon ionized the radicals. Spectroscopic constants were found for the $\bar{F} (3p)$ Rydberg state of the $CHF_{1}$ radical ($\nu_{\infty} = 49312(10) cm^{-1}$, $\nu_{2}^{\prime} (C-F Str) = 1358(15) cm^{-1}$, $\nu^{1}_{3} (CF_{2} scissors) = 680(20) cm^{-1}$, $\nu_{4}^{1} (OPLA) = 1022(8) cm^{-1})$ and of the $CDF_{2}$ radical $(\nu_{\infty} = 49323(10) cm^{-1}$, $\nu_{2}^{1} (C-F Str) = 1300(15) cm^{-1}$, $\nu^{1}_{3} (CF_{1} scissors) = 650(15)$ $cm^{-1}$, $\nu_{4}^{1} (OPLA) = 864(13)$ $cm^{-1})$. The REMPI spectra exhibited $\nu^{-}_{4} = 1-5$ hot bands of the $\bar{X} ^{2}{A^{\prime}}$ radical. Modeling of these hot bands with a quartic double-well potential gives the inversion barrier, $B_{IN} = 2800(500) cm^{-1}$, and $\Phi_{m} = 49(6)^{\circ}$.
Description
Author Institution: Chemical Kinetics and Thermodynamics Division, National Institute of Standards and Technology; Department of Environmental Chemistry and Biology, Johns Hopkins University School of Hygiene and Public Health