Chemical bonding properties in substituted disilynes
Abstract
The molecular structures of the Si₂HX, Si₂Li₂, SiGeHLi and C₂H₂ species (where X= H,
Li, F and Cl) were studied. All of these species have more than one isomeric form. The
critical points on the potential energy surfaces of the Si₂HX, Si₂Li₂ and C₂H₂ species and the minima on the SiGeHLi surface were located. The full six-dimensional potential
energy surface (PES) of the Si₂Li₂ molecule was calculated (for the first time) using the
CCSD(T)-F12a/cc-pVTZ-F12 level of theory.
The core-valence, zero-point energy and relativistic corrections for the Si₂HLi and
Si₂Li₂ species were calculated. Additionally, the electron affinity and Li⁺/H⁺ binding energies for the Si₂HLi and Si₂Li₂ structures were investigated. Furthermore, the anharmonic vibrational-rotational properties for the Si2HLi and Si₂Li₂ structures were calculated using second-order perturbation theory.
The recently developed CCSD(T)-F12a method with the cc-pVTZ-F12 basis set was employed to obtain geometries and relative energies (for the Si₂HLi, Si₂HF, Si₂HCl and Si₂Li₂ structures) and vibrational frequencies (for the Si₂H₂ and Si₂Li₂ structures). The
CCSD(T) method with the cc-pVXZ, aug-cc-pVXZ and aug-cc-pV(X+d)Z basis sets,
CCSD(T)-F12a/cc-pVXZ (where X=2-4) and the B3LYP/6-311+G(d) levels of theory
were also used. Comparison was made of the geometric properties and vibrational
frequencies calculated at the different levels of theory.
The calculated geometric properties for all the studied species and vibrational
frequencies (for the Si₂H₂ structures) show good agreement with the experimental and
theoretical literature.
The PES of Si₂Li₂ was used to perform large scale variational vibrational calculations
using the WAVR4 program. The first 2400 totally symmetric energy levels were
calculated. The low-lying energy levels were qualitatively correct. Conclusive
assignments of the vibrational modes of the Si₂Li₂ structures were made for the eleven
lowest lying energy levels.
Type
Thesis, PhD Doctor of Philosophy
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