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dc.creatorOka, T.en_US
dc.creatorEpp, Eriken_US
dc.description$^{a}$ M. Goto, B. J. McCall, T. R. Geballe, T. Usuda, N. Kobayashi, H. Terada and T. Oka, PASJ 54, 951 (2002) $^{b}$ T. R. Geballe, and T. Oka, unpublished $^{c}$ J. K. G. Watson, J. Mol. Spectrosc. 40, 536 (1973) $^{d}$ F. -S. Pan and T. Oka, ApJ 305, 518 (1986) $^{e}$ L. Neale, S. Miller, and J. Tennyson, ApJ 464, 516 (1996)en_US
dc.descriptionAuthor Institution: Department of Chemistry and Department of Astronomy and Astrophysics, the Enrico Fermi Institute, the University of Chicagoen_US
dc.description.abstractThe recent detection of the $R(3,3)^{l}$ absorption line of $H^{+}_{3}$ toward the Galactic center infrared sources GCS 3-2 and GC IRS $3 ^{a,b}$ has demonstrated a remarkable non-thermal rotational distribution of $H^{+}_{3}$. In cloud components which accommodates high $H^{+}_{3}$ column density on the order of $3 \times 10^{15} cm^{-2}$, the $(J, K) = (3, 3)$ level which is 361.5 K above the lowest (1,1) level is populated with a comparable abundance as the (1,1) level, while $H^{+}_{3}$ in the (2,2) level only 151.3 K above is not detectable. This highly non-thermal distribution is the result of a fast spontaneous emission $(2, 2) \to (1, 1)$ with the lifetime of 27.2 days due to centrifugal distortion induced dipole $moment^{c}$ and the metastability of the (3,3) level from which spontaneous emission is $forbidden.^{d}$ In order to understand the observed non-thermal distribution and to plan strategy for observing $H^{+}_{3}$ in higher metastable rotational levels (4,4), (5,5) and (6,6), we have conducted a model calculation on the $H^{+}_{3}$ equilibration in which spontaneous emissions and collision-induced rotational transitions are treated with steady state approximation. Accurately calculated Einstein coefficients of Neale, Miller and $Tennyson^{e}$ are used. Rates of collision-induced rotational transitions were estimated on the assumption of complete random collisional selection rules based only on the principle of detailed balancing. The results show that the preliminary observed values of $n(3,3)/n(1,1) \sim 1$ and $n(3,3)/n(2,2) \geq 5$ indicate an environment with high cloud temperature of $T \geq 300 K$ and low density $n(H_{2}) \leq 50 cm^{-3}$. They also suggest that observations of $H^{+}_{3}$ in higher metastable levels are realistic.en_US
dc.format.extent473580 bytes
dc.publisherOhio State Universityen_US

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