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Title: Electron correlations and two-photon states in polycyclic aromatic hydrocarbon molecules: A peculiar role of geometry

We present numerical studies of one- and two-photon excited states ordering in a number of polycyclic aromatic hydrocarbon molecules: coronene, hexa-peri-hexabenzocoronene, and circumcoronene, all possessing D{sub 6h} point group symmetry versus ovalene with D{sub 2h} symmetry, within the Pariser-Parr-Pople model of interacting π-electrons. The calculated energies of the two-photon states as well as their relative two-photon absorption cross-sections within the interacting model are qualitatively different from single-particle descriptions. More remarkably, a peculiar role of molecular geometry is found. The consequence of electron correlations is far stronger for ovalene, where the lowest spin-singlet two-photon state is a quantum superposition of pairs of lowest spin triplet states, as in the linear polyenes. The same is not true for D{sub 6h} group hydrocarbons. Our work indicates significant covalent character, in valence bond language, of the ground state, the lowest spin triplet state and a few of the lowest two-photon states in D{sub 2h} ovalene but not in those with D{sub 6h} symmetry.
Authors:
 [1] ;  [2] ;  [1] ;  [3]
  1. Department of Physics, University of Arizona, Tucson, Arizona 85721 (United States)
  2. Department of Physics, Indian Institute of Technology, Powai, Mumbai 400076 (India)
  3. (United States)
Publication Date:
OSTI Identifier:
22253474
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 10; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; CROSS SECTIONS; ELECTRONS; EXCITED STATES; GROUND STATES; NUMERICAL ANALYSIS; PARTICLES; PHOTONS; POLYCYCLIC AROMATIC HYDROCARBONS; POLYENES; SPIN; TRIPLETS