EXPERIMENTAL DETERMINATION OF THE $H_{3}O^{+}$ GROUND STATE INVERSION SPLITTING

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1985

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Ohio State University

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High resolution infrared spectra of the $1^{-} -O^{+}(10\mu m)$ $1^{+} -O^{-} (20 \mu m)$ and $1^{+} -1^{+} (27 \mu m)\nu_{2}$ vibration-inversion bands of $H_{3}O^{+}$ have been observed in an ac glow discharge by using tunable diode lasers and velocity modulation technique. The three band origins were found to be at 954.4003 (25) $cm^{-}$, 525.8237(13) $cm^{-1}$ and 373.2304(47) $cm^{-1}$, respectively. The rotational and centrifugal distortion constants of these three bands were also obtained from the least-squares fitting of observed transitions. From the molecular constants obtained above, we have determined the ground state inversion splitting of $H_{3}O^{+}$ molecular ion to be 55.3462 (55) $cm^{-1}$ and predicted the ground state inversion spectrum in the far IR region and the inversion-rotation spectrum in the millimeter wave region. These predictions may be used to detect this fundamental molecular ion in interstellar space. A comparison has been made between our experimental molecular constants and the relative strength of these three bands with those ab-initio theoretical predictions for this long-standing problem. The discharge chemistry of $H_{3}O^{+}$ is discussed with reference to the observed line strength - gas composition relation and known ion-molecule reactions.

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Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago

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