Knowledge Bank

The iodine UV fluorescence spectra originate from transitions between ion-pair states which behave Like $I+(1S)+I-(3P,1D,1S)$ at large internuclear separations and covalent states which dissociate into $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}P$ iodinec atoms. Even after a considerable experimental effort, the assignments of all the observed spectral features are not certain and there is a particular lack of data for the iodine ion-pair states. Ab initio effective core potential SCF + CI calculations for $I2$ have been combined with an empirical model for spin-orbit coupling to characterize the 23 covalent and 20 ion-pair valence states of molecular iodine. The important features of the $I2$ fluorescence spectrum between 260 and 410 nm have been determined from the calculated potential energy curves and transition moment data. Particular emphasis has been given to understanding the 340 nm emission. The effect of spin-orbit coupling on the observed fluorescence spectra will also be discussed.