DISILYNE (SI2H2) REVISITED

The singlet potential energy surface of Si2H2 has been explored by using ab initio theoretical methods. Complete geometry optimizations and vibrational frequency analyses were performed for 11 different structural isomers at the self-consistent field (SCF) and single and double excitation configuration interaction (CISD) levels of theory using double-ζ plus polarization (DZP) and triple-ζ plus double polarization (TZ2P) basis sets. Several extended basis sets including diffuse and higher angular momentum functions were employed in determining the final energetics of this system. Our analysis of the potential energy surface confirms that the global minimum is a C2v dibridged structure and reveals two minima and three transition states in the range 10-15 kcal/mol above the dibridged. We discuss the bonding character of the various isomers and identify the inert pair effect and the instability of the Si-Si π bonds as factors contributing to the relative stabilities. © 1990 American Chemical Society.