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A microscopic insight into oscillator strengths: The charge transfer bands for CuCl 2‐ 4
Author(s) -
Barriuso M. T.,
Aramburu J. A.,
Daul C.,
Moreno M.
Publication year - 1997
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(1997)61:3<563::aid-qua25>3.0.co;2-8
Subject(s) - character (mathematics) , atomic orbital , chemistry , charge (physics) , atomic physics , ligand (biochemistry) , wave function , molecular physics , extended hückel method , asymmetry , chemical physics , molecular orbital , physics , electron , quantum mechanics , molecule , geometry , biochemistry , mathematics , receptor , organic chemistry
The oscillator strengths f 1 , f 2 , and f 3 corresponding to the three allowed 2 e u , → 3 b 1 g , 3 e u → 3 b 1 g , and 1 b 2 u → 3 b 1 g charge‐transfer transitions of the D 4 h CuCl 2‐ 4 ‐complex together with their dependence on the metal‐ligand distance R are investigated using the self‐consistent charge extended Hückel (SCCEH) and MSXα methods. The main conclusions of this work are the following: (1) f 1 and f 2 directly reflect the σ‐character displayed by 2 e u and 3 e u orbitals. When this character is suppressed, f 1 and f 2 decrease by an order of magnitude and then become comparable to f 3 . This trend concurs with experimental findings. (2) The different σ‐character exhibited by 2 e u and 3 e u orbitals arises mainly from the 4 p (Cu) admixture. A similar one involving the 3 s (Cl) orbitals plays a minor role. When such admixtures are neglected, the two wave functions |2 e u 〉 and |3 e u 〉 can simply be written as |σ〉 + |π〉 and |σ〉 ‐ |π〉, respectively. The inclusion of 4 p (Cu), although small, produces an interference between |σ〉 + |π〉 and |σ〉 ‐ |π〉, enhancing the σ‐character in 2 e u and destroying it in 3 e u . This explains well the asymmetry between f 1 and f 2 observed experimentally. (3) The σ‐character in 2 e u and 3 e u together with f 1 and f 2 are found to be nearly independent upon R . (4) Also, the separation, Δ, between the energies of the 2 e u → 3 b 1 g and 3 e u → 3 b 1 g transitions was explored. It is shown that Δ is determined mainly by the ligand‐ligand interaction and, thus, is strongly dependent upon R . © 1997 John Wiley & Sons, Inc.