Molecular Physics seminar

Infrared spectrum of H3+ from the laboratory to the Galactic center

by Prof. Takeshi Oka (The University of Chicago)

FB53 ()


Protonated molecular hydrogen, H3+, is the simplest polyatomic molecule discovered by J.J. Thomson exactly 100 years ago. It is the most abundant molecular ion in hydrogen dominated plasmas and plays the central role in the formation of interstellar molecules. The infrared spectrum of H3+ discovered in the laboratory1 has led to its detection in 1996 toward two young stars deeply embedded in their natal dense clouds.2 Although it took many years to detect the first signal, once detected, H3+, has been observed everywhere. It was detected not only in dense clouds (n ~ 104 cm-3) as theoretically predicted but, surprisingly, also in diffuse clouds (n ~ 102 cm-3) where the abundant electrons were thought to destroy H3+. The most amazing discovery has been the very high abundance of H3+ in the Central Molecular Zone (CMZ), the region with radius ~ 200 pc, of the Galactic center. This has revealed a new category of gas with high temperature (~ 250 K) and low density (< 100 cm-3) with a high volume filling factor.3 Recent extension of this observation to wider regions of the CMZ4 will be discussed. 1 Oka, T. Phys. Rev. Lett. 45, 531 (1980) 2 Geballe, T.R. and Oka, T. Nature, 384, 334 (1996) 3 Oka, T., Geballe, T.R., Goto, M., Usuda, T. McCall, B.J. Astrophys. J. 632, 882 (2005) 4 Geballe, T.R. and Oka, T. Astrophys. J. 709, L70 (2010)