ULTRAVIOLET EMISSION SPECTRA OF THE HYDROGEN HALIDES

Abstract

Many-line spectra may be excited by electric discharges through the vapours of the hydrogen halides. In the case of HF, the long wavelength limit is about 2670 Å, and for HCl, about 2375 Å. So far, the spectra of HF, DF, HCl, DCl and HBr have been photographed, and those of HF, DF and HCl have been analyzed fairly completely. The bands, which possess simple P and R branches, are found to arise from the transitions V1∑+ — X1∑+, where X1∑+ is the ground state. The latter correlates with H + Halogen (2 P3/2): in the case of HF, it is believed that state V1∑+ correlates with H+ + F–. The internuclear distance in V is about twice that in the respective ground state, so that the observed lines correspond to transitions from low vibrational levels in V to high vibrational levels in X. In HF, predissoeiation by rotation is observed, leading to an accurate value for the dissociation energy.