Absorption Line Survey of H+3 Towards the Galactic Center.

We have conducted high-resolution (R = 20,000) spectroscopy toward sources in the Galactic center in search of absorption lines of H+3. The observation had been so far limited to the absorption lines from the lowest levels: (J, K) = (1, 0) of ortho-H+3 and (1, 1) of para-H+3. The wide wavelength coverage afforded by a cross-dispersing spectrograph enabled efficient spectroscopic survey of H+3 scattered in the 3 μm region. The survey leads to the first detection of H+3 in the metastable state in the interstellar medium. The R(3, 3)l at 3.543 μm, which is starting from the metastable (J, K) = (3, 3) state, are remarkable in that the line profile is distinctly different from those starting from the ground states. The H+3 absorption toward the Galactic center occurs in dense and diffuse clouds along the line of sight as well as the molecular complex close to the Galactic nucleus. We compare the line profiles of R(3, 3)l with those of CO first overtone at the 2.4 μm to discuss the nature of the clouds in which H+3 absorption from metastable state takes place. [ABSTRACT FROM AUTHOR]