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Self-Consistent Field Calculations of Hole States of Carbon Monoxide. Electron Density Functions by Computer Graphics Joseph Cambray,’” Johann Gasteiger,lbmCAndrew Streitwieser, Jr.,* I C and Paul S. Bagusld Contribution f r o m the Department of Chemistrjv, Unicersitj, of California, Berkele!., California 94720, and San Jose Research Laboratorj3, International Business Machines Corporation, San Jose, California. Receiced December 17, 1973 Ab inirio calculations using a moderately large basis set (double { plus polarization functions) are reported for various states of CO-, with emphasis on the core hole states, and CO. Three-dimensional perspective plots of electron density and difterence functions are used to visually study the validity of Koopmans’ theorem for core hole states and to probe associated electronic relaxation phenomena. Significant relaxation is associated with specific molecular environment ; valence orbital contraction is dependent on proximity to the core hole generated. Calculations were also performed on NO- and CFf in order to provide a qualitative visual evaluation of Jolly’s empirical ”equivalent cores” method. The results show that electron densities in bonds and at neighboring atoms do respond to a core hole approximately as if the core hole were a nuclear charge.
Abstract:
arbon monoxide is an extensively studied molecule, both theoretically a n d experimentally. The spectra of the ground state, many neutral excited states (valence and Rydberg), and several bound states of the positive ion have been tabulated.? More recently, uv7 and X-ray: photoelectron spectra have been reported for carbon monoxide. Photoelectron spectroscopy (ultraviolet, UPS,; and X-ray, XPS,6) has been applied t o developing the electronic structures of a wide variety of atoms a n d molecules. They have become effective probes into the ionization process a n d the generation of states not readily accessible by other techniques; this is especially true of states generated in XPS by ionization of a core electron leading to uni. positive atomic or molecular ions typically hundreds of electron volts above the ground state. In the past, various quantum mechanical models have been tested against the UPS and XPS results. XPS chemical shifts have been correlated with charge densities calculated using Pauling electronegativitiesC or semiempirical MO methods such as the extended H iickel treatment7 or the C N D 0 7 , 8prescription. These relationships generally suffice to give a qualitative picture of the ionized state, but cases have been found where charge densities, even when calculated by a
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( I ) (a) K.D.E.A. IV Prcdoctoral Fellow, 1971-1972; (b) NATO Postdoctoral Fellow, 1971-1972; (c) University of California; (d) Intcrnational Business Machines Corporation. ( 2 ) P. H. Krupenii., .%‘at. Sfuiiri. Ref Data Ser., .Vat. Bur. Staird., No. 5 ( I 966): this a o r k contains 278 references. (3) D. Vv, Turner and D. P. May, J . Chcni. Phj,s., 45, 471 (1966). (4) T. D. Thotiias,J. Chem. Phjs.,53, 1744(1970). ( 5 ) ( a ) D. W. Turner, C. Baker, A . D. Baker, a n d C. R . Brundle, troti Spectroscopy,” Interscience, New York, N . Y . , 1970; ( b ) S . D. Worlcy, Chenr. Rei.., 71,295(1971). (6) (21 I
