The band spectra of the lead halides, PbF and PbCI

Abstract

In the course of a series of investigations on the halides of Groups IV and V of the periodic Table, Howell and Rochester* reported that high-frequency discharges through the vapours of lead and bismuth Halides excited in each case large systems of bands degraded to the red and noted the striking similarity in general appearance of the spectra of corresponding lead and bismuth compounds. suck similarity was seen, especially when spectrograms of the fluorides or the chlorides were compared. Two of the lead Halides spectra, namely, those ascribed to the diatomic molecules PbF and PbCI, have been analysed and are described in the present paper. It is shown that their similarity to the corresponding spectra of the bismuth Halides is a consequence of the identity of the vibrational constants. No previous observations on the band spectrum of PbF appear to have been made. The Fluorescent spectrum of PbCI has been photographed and partly analysed by Popov and Neujmin, Using spectrographs of low dispersion (20 — 80 A per mm). The most satisfactory source of the spectrum of PbF was a high-frequency discharge through the vapour of the lead salt (pbF 2 ) in a quarts tube of the form shown in fig. 1.