Two- and three-photon absorption of iodine molecules via dissociative states

Abstract

Iodine vapor was irradiated by focused dye laser light in the range of 450–610 nm. Firstly, by irradiation of the laser light tuned near the dissociation limit of the B state (∼500 nm) emission bands were observed at 385, 342, 287, and 270 nm by two- or three-photon absorption. When the energy of laser light was above the dissociation limit of the B state, the emission intensity decreased drastically but was still observed. No effect of polarization of the laser light (circular or linear) was observed, indicating that the two-photon absorption is consecutive absorption of photons via dissociative states. Secondly, the absorption tuned far below the dissociation limit of the B state (550–600 nm) led to occurence of 342, 325, and 270 nm emission bands and IR emission at 1.3 μm originating from electronically excited iodine atoms I*(2P1/2). The excitation spectra of both UV and IR emission had the same threshold wavelength around 600 nm. The formation of the states responsible for the 325 and 270 nm bands is considered as three-photon absorption via the dissociative 0g+(1Σ) state that correlates to two I*(2P1/2) atoms.