Iodine, a test molecule in modern spectroscopy

Iodine, a diatomic molecule with especially attractive properties has been used for about a century to demonstrate new experimental techniques. Indeed, its convenient vapour pressure at room temperature, and its bright fluorescence spectrum, in spite of a relatively long lifetime in the excited state B make it very suitable for many optical and spectroscopic observations. Since the Faraday effect and the magnetic quenching observations of the beginning of the century, many experimentalists have worked with iodine. Recently, the advent of tunable dye lasers has made it possible to excite individual rovibronic states and to study their properties. This invention has been responsible for a minor revolution in molecular as well as in atomic spectroscopy. In this short article, we will review briefly the recent developments on absorption and fluorescence spectroscopy of iodine. Then, we shall present a review of the recent work through which by the patient disentangling of many threads, the elusive mechanism of the predissociation of the B state has been finally understood .at least within the precision of contemporary experiments.