Program: GN-2024A-FT-111

It has been discovered during the last two decades that the Central Molecular Zone (CMZ) of the Galactic center (GC), a disklike region of radius ~150 pc and thickness ~50 pc centered on the supermassive black hole, Sgr A*, is mostly filled by warm (~200 K) and diffuse (n ~ 50 cm^-3) molecular gas, which is expanding at speeds up to 150 km/s outward from the center. This vast and violent environment is unlike that of any diffuse clouds in the outer Galaxy. At present, the only molecular species observed in the diffuse CMZ, are CO at very low abundance and the molecular ion H3+. In the outer Galaxy, H3+ is known to be the starting point for the rich gas phase chemistry that results in the production of many molecular species observed in the interstellar medium. The presence of other species and hence the chemistry occurring in the CMZ’s diffuse gas, is unknown and unexplored. We propose to initiate the study of CMZ chemistry by using GNIRS to search for two infrared absorption lines of H2O on sightlines to infrared sources in the GC. The unique velocity profiles produced in the expandng CMZ diffuse gas will allow us to easily discriminate between absorption by gas in the CMZ and gas associated with clouds external to the GC.