To be or not to be: the early history of H 3 and H 3 +

Triatomic hydrogen became a major research area only after 1980, but its history goes back to J. J. Thomson's discovery in 1911. In fact, the possible existence of H(3) was suggested as early as 1895. This paper outlines the history of H(3) and H(3)(+) up to the mid-1930s, when chemists and physicists ceased to believe in the existence of the H(3) molecule. In the intervening years, there was a great deal of interest in 'active hydrogen' and also in the configuration of H(3), which was examined by Bohr in 1919. While H(3) was abandoned, H(3)(+) was not. Although the properties of H(3)(+) were largely unknown, the existence of the ion was firmly established, and its structure studied by means of the new methods of quantum chemistry.