Intensity Measurements in the Molecular Spectrum of Hydrogen

Abstract

Quantitative intensity measurements were made in the visible and infra-red of the ${\mathrm{H}}_2$ spectrum for different conditions in the discharge tube. The present paper reports on the Fulcher bands. It appears that at the lower pressures no equilibrium exists and that therefore the concept of temperature has no meaning. By varying the pressure and current in the discharge tube the effective rotational temperature can be varied from 240°K to 1500°K. Whereas higher rotational states are favored with an increase in pressure, the higher vibrational states are suppressed, and this effect is largely independent of the current. From the behavior of the relative intensities with pressure and current density conclusions can be drawn regarding the elementary processes in the discharge. The results show that extreme care must be used when intensity measurements in band spectra are used for temperature measurements. Apart from the fact that the conditions in the discharge tube may be far from equilibrium, our results on the $P$- and $R$-branches show that the transition probabilities may be quite different, even in simple bands, from the values predicted by the elementary theory.