Iodine 4d Research Articles

Trends in 4d-subshell photoabsorption along the iodine isonuclear sequence: I, I+, and I2+

The 4d absorption spectra of I, ${\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ have been observed in the 45--300-eV region using the dual laser-produced plasma technique. At lower energies each spectrum is dominated by intense 4d\ensuremath{\rightarrow}5p transitions, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared, where possible, with experiment. In the case of neutral iodine 4d\ensuremath{\rightarrow}6p transitions are also observed in the region close to the $^{2}$${\mathit{D}}_{5/2}$ threshold. The dominant feature in each spectrum, however, arises from 4d-f excitation, which evolves from a 4d-\ensuremath{\varepsilon}f shape resonance in neutral iodine to a feature containing discrete 4d\ensuremath{\rightarrow}nf transitions in ${\mathrm{I}}^{2+}$. \textcopyright{} 1996 The American Physical Society.

A theoretical CMS-X α treatment of CH3I photoionization dynamics: outer valence shell and iodine 4d levels

Abstract Continuum multiple scattering (CMS-X α) calculations are used to investigate methyl iodide photoionization dynamics. The validity of atomic versus molecular models of behaviour for the localised iodine 4d and 5p (lone pair) electrons, where conflicting experimental interpretations have been offered, is examined. A good account of all the available experimental data is obtained. While the calculations provide some limited support for an atomic-like description of the iodine 4d −1 phenomenological cross-section, the atomic picture has little validity for the 5p −1 ionization. Variations in both cross-section and β parameter which were previously ascribed to the Cooper minimum are identified to be more likely a core-valence shell interaction, opening above the 4d −1 threshold. The other valence shell channels are similarly affected. Significant l -wave mixing, induced by the molecular anisotropy, is found to result in the creation of mixed parity final states, contrary to the atomic model. In these circumstances odd and even harmonic components can interfere to create orientation (odd harmonic terms) in the photoelectron angular distribution (PAD). Molecule frame PADs are calculated and compared to experimental data for the ionization of oriented molecules, confirming an intuitive expectation of asymmetric electron emission from an asymmetric molecule. The CH 3 group therefore acts as a non-negligible perturbation, even on quite localised iodine 5p electrons, and the molecular environment is a paramount factor.

Fluorescence-photoion-coincidence spectroscopy on ICN core excited molecules

An experimental setup is presented to measure coincidence spectra between a fluorescence photon (260 nm≤λph≤600 nm) and one or two photoions after core excitation providing information about the dissociation channels leading to excited, fluorescing states. The dissociation of ICN molecules excited in the iodine 4d shell is discussed. Upon resonant excitation the intensity due to the parent ion is found to be negligibly small and the atomic fragments comprise the most important part of the fluorescence intensity. For the first time coincidences between one photon and two photoions have been measured. In general, the observed mean slopes of the double coincidence peaks are consistent with photoelectron-photoion-photoion) measurements on ICN. In the I+/CN+ channel the singly charged iodine atom is found with relatively high percentage in a different excited state than in the I+/C+ or I+/N+ channels.

Selectivity in the fragmentation of 1-bromo-2-iodoethane following iodine 4d core electron excitation

The selectivity in the fragmentation of 1-bromo-2-iodoethane after 4d iodine electron excitation has been investigated by TOF mass spectrometry, photoion—photoion coincidence and synchrotron radiation. Analysis of the results shows that the excitation of the I 4d 5/2,3/2 electrons into the lowest-energy empty σ* orbital leads to an enhancement of the CI and CBr bond breakages when the neutral core hole relaxes both into the mono- and the double-ionization continua. The results are discussed in terms of localization of the positive charges around the CI bond, which was originally excited through the resonances.

The absorption spectrum of CH3I in the extreme VUV

The absorption spectrum of methyl iodide has been photographed in the wavelength region 80-270 AA. Photoexcitation of the iodine 4d subshell was found to dominate the spectrum, giving rise to discrete 1A1 to 1A1, 1E transitions and a giant 4d to epsilon f continuum resonance. An analysis of the transitions is given and a value of 1.72+or-0.05 eV deduced for the 4d32/-4d5/2 spin-orbit splitting in the iodine atom.