OBSERVATION OF THE $3\nu_{2}\leftarrow 0$ OVERTONE BAND OF $H_{3}^{+}$

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Ohio State University

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We report the observation the second overtone $band^{1}$ $(3\nu_{2}(1=1)\leftarrow 0)$ of $H_{3}^{+}$ using a 1.45 $\mu m$ InGaAsP near infrared diode laser with the short external cavity mode control technique developed at McMaster $University.^{2}$ $H_{3}^{+}$ was generated using 1.5 Torr of $H_{2}$ with or without $4 \sim 5$ Torr of He in a liquid-$N_{2}$ cooled multiple-inlet-multiple-outlet discharge cell. The $H_{3}^{+}$ signal was detected with velocity modulation or ion concentration modulation in an AC glow discharge. Altogether four lines have been observed in the region of 6860--6925 $cm^{-1}$. The positions of the lines were determined using a wavemeter calibrated with $H_{2}O$ reference lines. The assignment of the transitions is based on Miller and Tennyson’s first principles $calculation^{3}$ and on observed temperature dependence of the relative intensities. Extended search of other transitions is being conducted. It is our hope that this observation may lead to detection of $H_{3}^{+}$ in higher vibrational states in Jupiter and other astronomical objects, and that it may also help in the assignment of the laboratory FTIR emission spectrum of hydrogen plasma.


$^{1}$S. S. Lee, B. F. Ventrudo, D. T. Cassidy, T. Oka, S. Miller, and J. Tennyson, J. Mol. Spec. 145, 222 (1991). $^{2}$D. T. Cassidy, Appl. Opt. 27, 610 (1988). $^{3}$S. Miller and J. Tennyson, private communication.""
Author Institution: Department of Chemistry and Department of Astronomy and Astrophysics, The University of Chicago; Department of Engineering Physics, McMaster University; Department of Physics and Astronomy, University College London