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A combined theoretical and experimental study of the ionic states of iodopentafluorobenzene
Univ Edinburgh, Sch Chem, Joseph Black Bldg,David Brewster Rd, Edinburgh EH9 3FJ, Midlothian, Scotland..
CNR IMIP, Lab Elettra, Trieste, Italy..ORCID iD: 0000-0003-4376-808X
CNR IOM, Lab TASC, Trieste, Italy..ORCID iD: 0000-0002-9491-0173
Aarhus Univ, Dept Phys & Astron, ISA, Ny Munkegade 120, DK-8000 Aarhus C, Denmark..
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2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 146, no 8, 084302Article in journal (Refereed) Published
Abstract [en]

A new synchrotron radiation photoelectron spectral (PES) study of iodopentafluorobenzene, together with a theoretical analysis of the spectrum, where Franck-Condon factors are discussed, gives detailed insight into the ionization processes, and this exposes the need for a reinvestigation of the vacuum ultraviolet spectral (VUV) assignments. We have calculated adiabatic ionization energies (AIEs) for several ionic states, using the equation-of-motion coupled cluster method for ionic states combined with multi-configuration self-consistent field calculation study. The AIE sequence is: (XB1)-B-2 < A(2)A(2) < (BB2)-B-2 < C2(2)B(1) < D(2)A(1) < E3(2)B(1). This symmetry sequence has a major impact on previous VUV spectral assignments, which now appear to be to optically forbidden states. Changes in the equilibrium structures for these ionic states are relatively small, but a significant decrease and increase in the C-I bond length relative to the X(1)A(1) structure occurs for the (XB1)-B-2 and (CB1)-B-2 states, respectively. The PES shows major vibrational overlaps between pairs of ionic states, X with A, and A with B. The result of these overlaps is the loss of vibrational structure and considerable broadening of the higher energy PES state. Although the baseline is nearly re-established between the A and B states, where the two bands are nearly separate, the B state is also broadened by the A state. Only the C ionic state, which shows the most highly developed vibrational structure, can be regarded as free from vibrational coupling to a neighbor state. The Franck-Condon analysis of the PES bands X, A, B, and C is described in detail; the apparent simplicity of some of these bands is illusory, since almost all the observed peaks arise from super-position of several calculated vibrational states. The experimental AIE of the A state, which is submerged under the X state envelope, has been determined by the subtraction of the calculated X state envelope from the observed PES spectrum. The overlap of these PES bands and the apparent closeness of the potential energy curves describing them have been investigated, using the state-averaged, complete active space self-consistent field method. We have identified two structures, one where the potential energy curves for the X and A states cross and another for the A and B states. At these two conical intersections (ConInts), there is zero-energy difference within each pair of states. Although similar in energy, the ConInt for the crossing of the X with A states, and that for the A with B states, shows that the open-shell occupancies correspond to the 4 lowest AIE states, and all four states that are quite different from each other. Published by AIP Publishing.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017. Vol. 146, no 8, 084302
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-320446DOI: 10.1063/1.4975672ISI: 000395901000022PubMedID: 28249445OAI: oai:DiVA.org:uu-320446DiVA: diva2:1091745
Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2017-04-27Bibliographically approved

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