In 1980, at the National Research Council of Canada, Oka discovered the infrared spectrum of H+ 3. which is thought to be the starting point for gas phase chemistry in interstellar "molecular clouds."[6] Following a lengthy search Thomas R. Geballe and Oka detected the infrared spectrum of H+ 3 in two interstellar clouds. Since then Oka and his colleagues have published numerous papers on their observations of interstellar H+ 3.
Tarsitano, Christopher G.; Neese, Christopher F.; Oka, Takeshi (2004). "High-resolution spectroscopy of the 22Πu←X4Σg− forbidden transitions of C2+". The Journal of Chemical Physics. 121 (13). AIP Publishing: 6290–6297. doi:10.1063/1.1787493. ISSN0021-9606. PMID15446923.
Gottfried, Jennifer L.; McCall, Benjamin J.; Oka, Takeshi (2003-06-22). "Near-infrared spectroscopy of H3+ above the barrier to linearity". The Journal of Chemical Physics. 118 (24). AIP Publishing: 10890–10899. Bibcode:2003JChPh.11810890G. doi:10.1063/1.1575737. ISSN0021-9606.
Goto, Miwa; McCall, Benjamin J.; Geballe, Thomas R.; Usuda, Tomonori; Kobayashi, Naoto; Terada, Hiroshi; Oka, Takeshi (2002-12-25). "Absorption Line Survey of H3+ toward the Galactic Center Sources I. GCS 3-2 and GC IRS3". Publications of the Astronomical Society of Japan. 54 (6). Oxford University Press (OUP): 951–961. arXiv:astro-ph/0212159. doi:10.1093/pasj/54.6.951. ISSN0004-6264.
McCall, B. J.; Hinkle, K. H.; Geballe, T. R.; Moriarty-Schieven, G. H.; Evans II, N. J.; Kawaguchi, K.; Takano, S.; Smith, V. V.; Oka, T. (2002). "Observations of H3+ in the Diffuse Interstellar Medium". The Astrophysical Journal. 567 (1). IOP Publishing: 391–406. arXiv:astro-ph/0110674. Bibcode:2002ApJ...567..391M. doi:10.1086/338380. ISSN0004-637X. S2CID118470478.