Electronic states and molecular constants of Bi2

Abstract

Potential energy curves of several electronic states of Bi2 have been calculated by the Rydberg–Klein–Rees method using molecular constants obtained from laser-excited photoluminescence of Bi2. These potential curves are used to compute Franck–Condon factors. Franck–Condon factors for the A–X system are compared with measured intensities of photoluminescence series extending over 50 vibrational levels (v″= 0–49) and including both Franck–Condon maxima. It is shown that more accurate molecular constants can be derived by using the information contained in these intensity data. Another important result is achieved by deriving previously unknown vibrational and rotational constants of the upper electronic state of the E–B doublet photoluminescence series using only line intensity measurements. Relative energy positions of the electronic states have been obtained by perturbation considerations and by measuring the temperature dependent changes of relative intensities of photoluminescence lines belonging to different electronic transitions. These experiments suggest that there is an electronic state X ′, which is lower in energy than the X state. A potential energy diagram for Bi2 is derived including the re-evaluated published spectroscopic data of Bi2.