Why is Si2H2 Not Linear? An Intrinsic Quasi-Atomic Bonding Analysis
- 12 August 2020
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 142 (32), 13729-13742
- https://doi.org/10.1021/jacs.0c03082
Abstract
The molecular energy of Si2H2 geometric structures increases in the order dibridged < trans-bent < linear, in contrast to acetylene, C2H2, for which the linear structure is the global minimum. In this study, the intra-atomic (antibonding) and bonding contributions to the total molecular energy of these valence isoelectronic molecules are computed by expressing the density matrices of the full valence space multiconfiguration self-consistent field wave function in terms of quasi-atomic orbitals. The analysis shows that the intra-atomic contributions to the molecular energy become less favorable in the order dibridged -> trans-bent -> linear for both C2H2 and Si2H2. By contrast, the inter-atomic bonding contributions become energetically more favorable in that order for both C2H2 and Si2H2. The two systems differ as follows. For Si2H2, the antibonding intra-atomic energy changes that occur when the dibridged molecule reconstructs into the trans-bent and linear structures prevail over the interatomic interactions that induce bond formation. In contrast, for C2H2, the interatomic interactions that create bonds prevail over the intra-atomic energy changes that occur when the dibridged molecule reconstructs into the trans-bent and linear structures. The intra-atomic energy changes that occur in these systems are related to the hybridization of the heavy atoms in an analogous manner to the hybridization of C in CH4 from (2s)(2)(2p)(2) to sp(3) hybrid orbitals.Funding Information
- Division of Chemistry (CHE-1147446)
- Basic Energy Sciences (DE-AC02-07CH11358)
- National Science Foundation (ACI-1047772)
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