On the ground state of (H2), the molecular Ion (H2 +) and wave mechanics

It is not, I think, very generally known how accurate the check between the results of wave-mechanics calculations and the experimental data is, which is afforded by the fundamental constants of the H2 molecule. In all probability this is partly because the improvements in the determinations of the various quantities have been made in an uncoordinated way by people largely interested in divers questions and partly perhaps to some small inaccuracies in the published data. However all this may be, the present time seems opportune for a critical discussion of this question. There are various ways in which such tests can be carried out, but the most exact is by means of the following energy relation: Spectroscopic ionization potential of (H2) + total negative energy of the molecular ion (H2+) = total negative energy of (H2) = total negative energy of 2(H) atoms + dissociation energy of (H2). The total negative energy of (H2+) is got from the wave mechanics by solving Schroedinger's equation for this structure and the total negative energy of an (H) atom is equal to R, the Rydberg constant. So far as anything pretending to accuracy is concerned the spectroscopic ionization potential of H2 is an experimental quantity, being got from the analysis of the H2 spectrum. The spectroscopic value is, however, confirmed by the results of an electrical determination by Bleakney. Until recently the only reliable determinations of the dissociation energy D of H2 were also experimental. D is the least accurately determined of these four quantities. The best experimental values until about a year ago were probably D = 4·55 ± 0·16 electron volts by Bichowsky and Copeland (1928) and D = 4·34, with about similar accuracy, by Witmer (1926).