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Ab initio molecular orbital and density functional study of the C 6 H 6 ⋅I 2 complex in the ground and excited electronic states
Author(s) -
Mebel A. M.,
Lin H. L.,
Lin S. H.
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)72:4<307::aid-qua13>3.0.co;2-e
Subject(s) - excited state , ab initio , chemistry , atomic physics , excitation , ground state , density functional theory , ab initio quantum chemistry methods , molecular orbital , molecular physics , electronic structure , molecule , computational chemistry , physics , quantum mechanics , organic chemistry
The structure and energetics of the C 6 H 6 ⋅I 2 complex have been studied using the density functional B3LYP and ab initio second‐order Møller–Plesset (MP2) and coupled cluster CCSD(T) methods with quasirelativistic effective core potential on iodine atoms and various basis sets. The calculations in the ground electronic state consistently favor the “unsymmetrical” oblique structure 1 ( C s ). The axial structure 2 ( C 6 v ) is found to have two imaginary frequencies and to represent a second‐order hilltop. The energy difference between 1 and 2 is predicted to be of about 1 kcal/mol, so the potential energy surface is extremely flat and the I 2 molecule can easily undergo a large‐amplitude torsional motion. The CIS calculations showed that in the excited charge‐transfer (CT) states the complex geometry dramatically changes. The 1 A ′ CT state which possesses the largest oscillator strength is found to have a “resting” structure. The CT states (4 1 A ′ and 3 1 A ″) of C 6 H 6 ⋅I 2 lie between the local excitations related to the 1 Π g and 1 Δ g states of iodine and significantly higher in energy than the 1 Π u local excitation of I 2 . The broad character of the experimental CT absorption band is explained on the basis of the large (1.55 eV) difference between the vertical and adiabatic excitation energies of 4 1 A ′ and the dramatic geometry change in the CT state. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 307–318, 1999