Multiphoton Laser Spectroscopy of Indium Monoiodide

The laser induced fluorescence (LIF) and the multiphoton ionization (MPI) spectra of indium monoiodide have been obtained at ultraviolet and visible wavelengths. Fluorescence from excited indium atoms at 451.1 nm (6s ^2 S_{1/2} to 5p ^2P_ {3/2}) is produced by the multiphoton dissociation of InI. The LIF spectrum contains resonances corresponding to transitions between the ground state, X 0^+ (^1Sigma _sp{0}{+}), and the second excited electronic state, B 1 (^3Sigma _1). Seven previously unreported bands, (4-0), (5-1), (6-2), (3-0), (4-1), (5-2), and (6-3), were observed. Transitions to the first exicted electronic state, A 0^+ (^3 Sigma_sp{0}{+}), do not appear, indicating that two-photon photodissociation at those wavelengths does not occur. Analysis of the vibrational resonances and suppressions show that the ground state dissociation energy lies between 25 430-25 140 cm ^{-1} (3.153-3.117 eV) as compared to the commonly accepted value of 27 700 cm^ {-1} (3.43 eV). Suppression of fluorescence spectroscopy of the excited state of indium has revealed the fine structure splitting of np ^2P states. Energy differences were measured up to n = 17 and agreement was found with previous measurements. Three splittings were previously unreported (n = 15-17) and were found to agree with predicted values. Multiphoton ionization of InI involves not only the direct ionization of the molecule, but the production of ion pairs In^+ and I ^- and the ionization of neutral photofragments produced by multiphoton dissociation. Ground, metastable and excited state indium atoms produced by one-, two- and three-photon dissociation are ionized by the aborption of additional photons. Ion-pair production was found to be the most prominent process as it requires the fewest number of photons, but multiphoton dissociation into neutrals was effective in limiting ionization. Photodetachment of the electron from I^- was found to significantly enhance the A(2-0) band resonances in the MPI spectrum at 404.5 and 404.8 nm.