The spectrum of fluorine (FI)

The investigations of the spectrum of fluorine which had been made up to the year 1923 are summarised in Kayser’s ‘Handbuch der Spektroscopie’ (vol. 5, p. 444; vol. 7, p. 401). They include measurements of lines attributed to fluorine by various workers, but there is no attempt to classify the lines of the neutral atom, the singly ionised atom, etc. Gale and Monk, however, have since published further measures of fluorine lines, and have made the beginnings of a classification by distinguishing the lines produced in vacuum-tube discharges through fluorine gas from those obtained only from a spark discharge in the gas at atmospheric pressure: Their work has been followed up by Carragan, who has made a study of the Zeeman effects for some of the lines of the former group, and, from the rules of Landé, has deduced the existence of multiplets of the first order and suggested certain term combinations. The results here recorded are the first-fruits of an investigation of the fluorine spectrum under different conditions of excitation. Evidence of at least three successive spectra has been obtained as the exciting agency is gradually intensified. Under the gentlest stimulus the lines which appear form an isolated group in the red and infra-red region of the spectrum. They are in the main identical with the vacuum-tube lines of Gale and Monk, and have been produced simultaneously with strong bands of silicon tetrafluoride when a discharge has been passed through this gas. They have accordingly been assigned to the neutral atom of fluorine. The identification, measurement and classification of these lines form the substance of the present paper. Data concerning the spectra produced by more intense discharges will be published in due course.