The emission spectrum of bismuth fluoride (BiF)

Abstract

The most probable electron configuration of the lighter diatomic molecules and the order of their electrons binding have been determined by Mulliken, but no such systematic scheme has yet been formulated for the heavier molecules. The reason for this is not far to seek. the molecules whose structure can best be interpreted theoretically are H 2 and He , and with these providing a secure foundation the successive addition of single electrons to them has enabled the configuration of the simpler molecules to be determined. This process, similar to the Atombau method used by Bohr, cannot be continued indefinitely as its successful working depends entirely on the existence of suitable molecular data. These are derived mainly from the vibrational and rotational analyses of band spectra and also from ionization potential experiments. At present comparatively few measurements have been made upon the spectra of heavy diatomic molecules and these have been used to provide vibrational analysis only. It is this incompleteness in the observational data that is hindering the construction of a reliable electronic scheme for these molecules. In building up the configuration of the members of such a series as AuF, HgF, TlF, PbF, and BiF where the atomic number of the metal radical increases by unity from member to member, the most that can be expected at first is a determination of the change in the binding force from molecule to molecule as the additional electron is added. This change can be followed by noting the change in the vibration frequency of each molecule in its ground state. This series was chosen on account of a very remarkable similarity in the general appearance of the spectra of PbF and BiF, which has been reported in a previous publication.