Quantum chemical calculations on SiF4 and it's protonated analogues

Abstract: For every heteronuclear molecule, protonation can occur at more than one site

thus giving rise to more than one proton affinity. Experimentally, only one proton affinity

(PA) value is reported for a molecule and the experiment does not specify the site for the

protonation. In the present work, quantum chemical calculations are carried out on SiF4 and

its possible protonated analogues (HF4Si+ and HSiF4

) by employing several computational

chemistry methods including the MP2 method with 6-311++G** and cc-pVDZ basis sets,

the HF, B3LYP and the CCSD methods with the 6-311++G** basis set and the Gaussian 04

(G4) compound method with the aim of determining the protonated analogue that

corresponds to the experimentally determined PA value. Also, bond distances, bond angles,

rotational constants, dipole moments, infrared spectroscopy and HOMO-LUMO energies are

calculated for the three molecular species; SiF4, HF4Si+ and HSiF4

. From the results, the

experimentally reported PA value is found to correspond to the protonated analogue in which

the proton is attached to one of the fluorine atoms (HSiF4

) instead of the one in which the

proton is attached to the silicon atom. Except for the HOMO-LUMO energies which are best

predicted by the B3LYP method, other parameters are found to be accurately predicted by

the G4 compound method in comparison with available experimental results. These findings

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