title: Interpretation of the vacuum ultraviolet photoabsorption spectrum of iodobenzene by ab initio computations.
abstract: Identification of many Rydberg states in iodobenzene, especially from the first and fourth ionization energies (IE1 and IE4, X(2)B1 and C(2)B1), has become possible using a new ultraviolet (UV) and vacuum-ultraviolet (VUV) absorption spectrum, in the region 29 000-87 000 cm(-1) (3.60-10.79 eV), measured at room temperature with synchrotron radiation. A few Rydberg states based on IE2 (A(2)A2) were found, but those based on IE3 (B(2)B2) are undetectable. The almost complete absence of observable Rydberg states relating to IE2 and IE3 (A(2)A2 and B(2)B2, respectively) is attributed to them being coupled to the near-continuum, high-energy region of Rydberg series converging on IE1. Theoretical studies of the UV and VUV spectra used both time-dependent density functional (TDDFT) and multi-reference multi-root doubles and singles-configuration interaction methods. The theoretical adiabatic excitation energies, and their corresponding vibrational profiles, gave a satisfactory interpretation of the experimental results. The calculations indicate that the UV onset contains both 1(1)B1 and 1(1)B2 states with very low oscillator strength, while the 2(1)B1 state was found to lie under the lowest ππ(∗) 1(1)A1 state. All three of these (1)B1 and (1)B2 states are excitations into low-lying σ(∗) orbitals. The strongest VUV band near 7 eV contains two very strong ππ(∗) valence states, together with other weak contributors. The lowest Rydberg 4b16s state (3(1)B1) is very evident as a sharp multiplet near 6 eV; its position and vibrational structure are well reproduced by the TDDFT results.
authors: School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, Scotland, United Kingdom.
authors: Michael H
authors: MH
authors: Palmer
authors: School of Chemistry, University of Edinburgh, Joseph Black Building, David Brewster Road, Edinburgh EH9 3FJ, Scotland, United Kingdom.
authors: Trevor
authors: T
authors: Ridley
authors: Department of Physics and Astronomy, ISA, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
authors: Søren Vrønning
authors: SV
authors: Hoffmann
authors: Department of Physics and Astronomy, ISA, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark.
authors: Nykola C
authors: NC
authors: Jones
authors: CNR-ISM, Montelibretti, c/o Laboratorio Elettra, Trieste, Italy.
authors: Marcello
authors: M
authors: Coreno
authors: CNR-IOM Laboratorio TASC, Trieste, Italy.
authors: Monica
authors: M
authors: de Simone
authors: CNR-IOM Laboratorio TASC, Trieste, Italy.
authors: Cesare
authors: C
authors: Grazioli
authors: National Research Council ICCOM-CNR, UOS di Pisa, Via G. Moruzzi 1, I-56124 Pisa, Italy.
authors: Malgorzata
authors: M
authors: Biczysko
authors: Scuola Normale Superiore, Piazza Cavalieri 7, 56126 Pisa, Italy.
authors: Alberto
authors: A
authors: Baiardi
authors: Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal.
authors: Paulo
authors: P
authors: Limão-Vieira