Photoabsorption of the molecular IH cation at the iodine 3d absorption edge

Abstract

Yields of atomic iodine Iq+ (q≥2) fragments resulting from photoexcitation and photoionization of the target ions IH+ and I+ have been measured in the photon-energy range 610-680 eV, which comprises the thresholds for iodine 3d ionization. The measured ion-yield spectra show two strong and broad resonance features due to the excitation of the 3d3/2,5/2 electrons into ϵf states rather similar for both parent ions. In the 3d pre-edge range, excitations into (npπ)-like orbitals and into an additional σ∗ orbital are found for IH+, which have been identified by comparison of the atomic I+ and molecular IH+ data and with the help of (time-dependent) density functional theory (DFT) and atomic Hartree-Fock calculations. The (5pπ) orbital is almost atomlike, whereas all other resonances of the IH+ primary ion show a more pronounced molecular character, which is deduced from the chemical shifts of the resonances and the theoretical analysis.