Takeshi Oka’s studies are concentrated in astrochemistry, an interdisciplinary field unifying astronomy and chemistry. His team discovered long-chain cyanoacetylene molecules HC5N, HC7N and HC9N, and initiated interstellar carbon chain chemistry. This work has been revived recently in the studies of diffuse interstellar bands.
The abundance of those molecules led him to the studies of interstellar H3+, which plays the central role in interstellar chemistry. Takeshi uncovered the laboratory infrared spectrum of H3+. Using the spectrum, he detected interstellar H3+ in dense molecular clouds after 16 years of search with Thomas R. Geballe. This established the central idea of ionic reactions for producing interstellar molecules.
Takeshi’s subsequent observations revealed unexpected large amount of H3+ in diffuse clouds and demonstrated that cosmic ray flux is ten times higher in diffuse clouds than in dense clouds. He discovered a high abundance of H3+ near the galactic centre (GC) and demonstrated the presence of a vast amount of expanding warm and diffuse gas, which dominates the region. This has radically changed previous concepts of the gas near the GC.