Optical dissociation of iodine molecules is demonstrated by absorption by the atoms of light of wave-lengths 1830, 1783, 1642, 1618, 1583 and 1515A these being the lines in the region 2100 to 1514 which arise from transitions to the normal state of the iodine atom. This dissociation is produced in iodine-argon mixtures by light of wave-length >5100A, which produces only excited molecules immediately upon absorption so that the atoms presumably result from dissociation produced by collisions. Spectra of electrical excitation and of fluorescence in iodine-argon mixtures show that molecules of higher $v^{\prime }$ are more effectively quenched, this larger quenching setting in at about $v^{\prime }=12\mathrm{}$. This suggests that the effect is a sort of predissociation, enhanced by collisions. A possible theoretical interpretation of such an effect is discussed.

• Received 5 July 1932

DOI:https://doi.org/10.1103/PhysRev.41.627