Chemical bonding properties in substituted disilynes

• Main Author: Serafin, Lukasz Michal
• Other Authors: van Mourik, Tanja; Law, Mark M.
• Published: University of St Andrews 2012
• Subjects: 661.08
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.574761

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, Si2Li2and 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.