ASSIGNMENT OF THE $2\nu_{2}$ BAND OF THE $H^{+}_{3}$ ION IN EMISSION

$^{1}$ W. A. Majewski, M. D. Marshall, A. R. W. McKellar, J. W. C. Johns, and J. K. G. Watson, J. Mol. Spectrosc. 122, 341--355 (1987). $^{2}$ S. Miller and J. Tennyson, J. Mol. Spectrosc. 128, 530--539 (1988). $^{3}$ M. G. Bawendi, B. D. Rehfuss, and T. Oka, Paper RA10, 43rd Symposium on Molecular Spectroscopy, Columbus, Ohio (1988). $^{4}$ S. Miller and J. Tennyson, J. Mol. Spectrosc., to be published. $^{5}$ J.-P. Maillard and P. Drossart, personal communication.Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada; Department of Physics and Astronomy, University College LondonIn a search for the $2\nu_{2}$ band of the $H^{+}_{3}$ ion in emission the region $4500-5200 cm^{-1}$ of the spectrum was recorded in 1985, employing the hollow-cathode electrical discharge cell previously used to observe the $\nu_{2}$ fundamental in emission$1$. However, the high rotational temperature of the $H_{3}^{+}$ ions prevented a rotational analysis until high-quality ab initio predictions became available in $1988_{2}$ and were tested against the difference band $2\nu_{2} - \nu_{2}$ by Bawendi, Rehfuss and $Oka^{3}$. These ab initio calculations have now been $extended^{4}$ to higher values of J, and have made it possible to assign more than 50 of the observed lines to rotational transitions of this band. The rotational temperature is found to be approximately 1800 K. By a comparison with the laboratory spectrum, more than 20 emission lines observed from one of the polar `hot spots' in the auroral zone of $Jupiter^{5}$ have been assigned as belonging to this band, giving the first definitive observation of extraterrestrial $H_{3}^{+}$