Protonated disilyne, Si2H+3: Molecular structures, vibrational frequencies, and infrared intensities.

The singlet potential energy surface of protonated disilyne, Si2H+3, has been investigated theoretically using the self-consistent field (SCF) and configuration interaction (CI) methods. Complete geometry optimizations and harmonic vibrational frequency analyses were performed using a double-ζ plus polarization (DZP) basis set at both the SCF and CI levels of theory. Five minima were located, with the global minimum being a highly symmetric tribridged structure. There are three minima clustered at 11–15 kcal/mol higher in energy. One of these has two bridging hydrogen bonds, another has only one and the third has none at all. A trans-bridged isomer is a higher-lying minimum. Structures corresponding to the classical and nonclassical forms of the vinyl cation, C2H+3, are shown not to be minima. Final energetic predictions are made using several extended basis sets which are at least triple-ζ plus double polarization (TZ2P) in quality. Inclusion of electron correlation is found to be very important for energetic comparisons, geometries and characterization of the stationary points. The theoretical infrared intensities may be useful in the spectroscopic identification of Si2H+3. [ABSTRACT FROM AUTHOR]