Three Photon Resonance Enhanced Absorption Spectroscopy of ¹²⁷I₂ and ¹²⁹I₂

Abstract

<p>The construction and development of a laser spectrometer designed to generate multiphoton spectra is outlined. This apparatus has been used successfully to record the resonance enhanced three photon absorption spectrum of the isotopic molecules, ¹²⁷I₂ and ¹²⁹I₂.</p> <p>Multiphoton spectra have been obtained under low (Δν~1.0 cmˉ¹) and high (Δν ~ 0.12 cmˉ¹) resolution, by monitoring the undispersed fluorescence from highly excited states, following dye laser excitation over the green-red portion of the visible spectrum. The high resolution spectra were obtained either through the use of a single tunable dye laser or alternatively with the use of two dye lasers in tandem. In addition, spectra have been obtained for the first time using a dye laser configuration which allowed it to oscillate at two separate frequencies simultaneously, one of which was tunable.</p> <p>The analysis of the high resolution spectra for both molecules has given evidence for at least five different excited states in the 50000-55000 cmˉ¹ region as being responsible for the observed spectrum. A detailed rotational analysis has been possible for three of these states, all of which are shown to be ion-pair in nature and of 0⁺μ symmetry. No prior rotational analysis has been given for one of these states (the F0⁺μ (³P₀)). The high resolution analysis was facilitated by measuring the polarization dependence of the rotational transitions under linearly and circularly polarized excitation. Isotopic substitution has allowed; the assignment of absolute vibrational numbers.</p> <p>The results of several investigations by previous workers are also incorporated into the analyses presented in this study. Conclusions are drawn that raise serious doubts about the validity of earlier reports concerning the existence of bound states lying near 35000 cmˉ¹ above the ground state.</p>