Multiphoton absorption spectroscopy of iodine

Abstract

<p>Two independently tunable excimer laser pumped dye lasers have been used to examine the high resolution (Δυ~0.1 cm⁻¹) three-photon absorption processes for the isotropic molecules, ¹²⁷I₂ and ¹²⁹I₂. Multiphoton spectra have been obtained by monitoring the undispersed fluorescence from highly excited states, either through the use of a single tunable dye laser (3P1C) or with the use of two dye lasers in tandem (3P2C). Four separate electronic states accessed by a 3-photon (3P) process have been observed in the 47000-60000 cm⁻¹ energy region. A detailed rotational analysis has been possible for the four states, three of which are shown to be of ion-pair character and oᵤ⁺ symmetry. The fourth state is shown to be of extra-valence (Rydberg) character and of oᵤ⁺ symmetry. This later state is reported for the first time and it is one of the few Rydberg states to be analysed rotationally. The results of several previous studies are incorporated into the analyses, and reinvestigation of unanalysed MPI spectra reported by other workers is discussed and analysed in this study.</p>