ABSTRACT
From the earliest days of mass spectrometry, ions were observed which generally were agreed to have arisen from reactions between ions and neutral molecules. An ion of m/z 3 was observed by Dempster^ in 1916 and identified as ; its formation by Reaction 1 was well established by 1925.^^ ^ In 1928,
a : + H2 - > H 3 + H (1)
Hogness and Harkness^ reported the formation of and 13" in iodine vapor subjected to electron impact. lon/molecule reactions were observed in several other systems during the 1920s; the early work has been reviewed by Smyth^ and by Thompson.^ With improvements in instrumentation and techniques, particularly vacuum technology, the nuisance of secondary processes was largely eliminated, and studies of ion/molecule reactions largely ceased. The main interests in mass spectrometry during the period 1930 to 1950 lay in the physics of ionization and dissociation, in the determination of isotopic masses and abundances, and in the development of analytical mass spectrometry using primarily electron ionization.
