The recently introduced set of the quadratic, two-electron covalent and ionic valence indices is used to investigate the bond-breaking-bond-forming (BB-BF) process in an atom exchange reaction between H2 and X (X = H, F-I) as well as in the 0 2 -H system. Valence changes accompanying selected charge reorganizations are examined within the three-orbital model and valence diagrams for symmetric transition states (TSS) are given. The UHF valence data for Liz0 and C02 and the H-H-X, 0-0-H, and 0-H-0 (ABC) TSS (collinear and angular) are reported and compared to valence data in the separated fragments limits (SFL), AB and BC. The overall valence, v ( A B C ) , and the total (ionic plus covalent) diatomic valences, and v~c, are used as measures of the overall bond-order in a concerted BE-BF reaction, to test the postulate of the bond-energy-bond-order (BEBO) model. In collinear TSS of H2X, 7 / = -I , i.e., one bonding electron pair, is found to be roughly preserved, whereas in the angular H2X and in collinear 0-H-0 TSS, the effect of increased valence at the saddle-point is observed, relative to that of diatomic fragments (reactants or products). For the angular 0-0-H TS, a similar increase in I v ( A B C ) J relative to both 0 2 and OH s n s is detected; smaller changes relative to the 0 2 data are found in the collinear TS. This observation is in agreement with earlier predictions from the intersecting-state model. The relative diatomic valences, v: ; / v: F and %'$/-viF, are shown to conserve the overall relative bond multiplicity around 1 in both collinear and angular TSS of the H2-X systems. 0 1994 John Wiley & Sons, Inc. qo = {PEP (p} = qo.ff + qO'P. These reference occupations and the associated atodion electron populations, no = {I: 4:) (the summation is over all OAOS of atom A), define the respective occupatiodpopulation displacements: AqP = P -0 , P 9 q . ( 3 ) 0 An = nno, The explicit expressions for the QVIS are defined as follows [l]:Aq = qq , Aq" = qff -qo3",
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.