K. Kawaguchi, Y. Kasai, S.-I. Ishikawa, M. Ohishi, N. Kaifu, and T. Amano
Detection of a new Molecular Ion HC3NH+ in TMC-1,
Astrophys. J. 420, L95 L97 (1994).
The J" = 3 and 4 transitions near 34.6 and 43.3 GHz were detected in emission using the Nobeyama 45 m dish.