Laser photoluminescence of Bi2

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Abstract
Bismuth diatomic molecules are produced in an inert gas flow system and in a heat‐pipe oven at pressures from 10−4 to 10 torr. Photoluminescence of Bi2 has been studied with various laser sources and with white light. Strong photoluminescence is due to different vibrational–rotational transitions of the A–X system. Observed weaker photoluminescence series are due to vibrational–rotational transitions of four previously unknown electronic systems of Bi2 with ωe= 154.29±0.45 cm−1; ωe=141.23±0.35 cm−1; ωe=127.05±0.1 cm−1 and ωe=105.68±0.25 cm−1. Long v″ progressions extending over the whole Franck–Condon distribution (including both maxima) are measured for several electronic transitions. Molecular constants for the lower electronic states involved are obtained from spectroscopic analysis. The laser‐excited photoluminescence experiments suggest that A is not the first excited state in Bi2 and that X is not the ground state of Bi2 but that the X ′ state is probably the lowest energy state. Photoluminescence with white light excitation consists of emission from Bi2 and atomic Bi. In addition to discrete line photoluminescence, continuum spectra arising from an unbound upper state are observed with 514.5 nm laser excitation and with white light excitation.