Program: GS-2010A-C-3

Following up our exciting discovery this summer at the Gemini South Observatory of large column densities of H$_3^+$ with extremely rich velocity profiles toward newly observed sight lines to the Galactic center, we propose to use the Phoenix Spectrometer to further obtain high resolution spectra of H$_3^+$ and CO on these sight lines. So far our observations have been limited to H$_3^+$ in the lowest ($J$, $K$) = (1, 1) rotational level, but extension to higher rotational levels (1, 0), (2, 2), and particularly the metastable (3, 3) level will allow us to obtain detailed information on the physical and chemical nature of the gas in the Central Molecular Zone (CMZ) of the Galaxy. For one sightline near Sgr B which showed a particularly rich spectrum and high temperature, we will also attempt to detect H$_3^+$ in higher metastable levels. So far our understanding of the gas in the Central Molecular Zone (CMZ) has been limited to the central region from the center to 30 pc to the East, but the proposed observation using the new sight lineds will provide a more general picture of the gas as the new targets span a much wider region of the CMZ, from 100 pc East to 140 West of Sgr A*.