Investigation of the density-functional theory-derived scaled quantum mechanical method for cage-like systems:: the vibrational analysis of adamantane

The Becke3-Lee-Yang-Parr(B3-LYP)/6-31G* derived scaled quantum mechanical (SQM) method has been investigated for cage-like systems using adamantane as the model molecule. The original scale factors were found to transfer well to adamantane except the general heavy atom scale factor for the CC stretching modes of the skeleton. For these vibrations a new individual scale factor was developed in the present study. A complete vibrational analysis of adamantane and adamantane-d(16) has been performed. The experimental vibrational spectra of the compounds were reinterpreted using the scaled B3-LYP/6-31G* harmonic force field. Some assignments of earlier less sophisticated investigations have been revised, and reliable predictions for the IR and Raman inactive fundamentals are proposed.