Vibrational spectra of triamantane X18H24, iso-tetramantane X22H28 and cyclohexamantane X26H30 (XÂ =Â C, Si, Ge, Sn) - A theoretical study

Optimized geometrical parameters are obtained for triamantane, iso-tetramantane and cyclohexamantane (X = C, Si, Ge, Sn) using B3LYP method with 6-311G** and/or LANL2DZ basis set. For carbon compounds Hartree-Fock (HF) method is also used for the study. The harmonic vibrational frequencies are obtained for all the molecules at their respective optimized geometries. The calculated adamantane frequencies are fitted to the experimental ones of adamantane-d0 molecule to get the scale factors for C-H stretching frequencies. For all the other modes the scale factors obtained earlier [G. Ramachandran, S. Manogaran, J. Mol. Struct. THEOCHEM, 766 (2006) 125] by fitting all the isotopomers are used. The scale factors thus obtained are used to predict the fundamental frequencies of all carbon compounds and compared to the available experimental Raman frequencies. The assignments are proposed for all fundamentals of the title compounds using normal coordinate analysis.