Fine structure in the arc spectra of bromine and iodine

Abstract

The fine structures of a number of bromine arc and spark lines have been previously reported by Hori, who examined the emission lines given by a spark discharge through a capillary tube, a small transmission echelon being employed to observe the structures. He found that four of the strongest lines in the red region had similar structures, each showing four components degrading in intensity and interval to the short wave-length side. The intervals in the four lines, though not identical, were fairly close to one another. De Bruin assumed that these four lines, which come to the 5 s . 4 P 3/2 term, have identical structures which are characteristic of that term. Since the lines are quartet, he suggested that the nuclear spin is 3/2. As supporting evidence he took the mean value of the four line structures as being the term structure and pointed out that the interval ratios corresponded to this value of the spin. An account is given here of further observations in the bromine arc lines, the structures being considerably extended by the use of a high frequency electrodeless discharge in pure bromine vapour and a Fabry-Perot interferometer of variable plate separation. Although it is shown that de Bruin’s assumption as to the equality of these four structures is incorrect, the spin of 3/2 is confirmed. It is further shown that the two isotopes of bromine (79, 81) have the same nuclear spin.