At −180° C the absorption spectrum of uranyl compounds has one band in common with the emission spectrum (cf. fig. 2). At room temperature, however, a new band appears in the absorption spectrum on the red side, having the same wave‐length as the dominant band of the emission spectrum, while a new band also appears in the emission spectrum on the violet side, at the same wave‐length as the principal absorption band (cf. fig. 2). This behaviour can be explained by means of the potential curves of fig. 1, giving the energy content of the UO2++ion as a function of the U‐O distance. At −180° C absorption starts only from the level 00. Temperature equilibrium is reached wit