A VIBRATIONAL ASSIGNMENT OF ADAMANTANE AND SOME OF ITS ISOTOPOMERS - EMPIRICAL VERSUS SCALED SEMIEPIRICAL FORCE-FIELD

Raman and infrared spectra of adamantane-d(0) and several of its isotopomers (adamantane-1-d(1), adamantane-2-d(1), and adamantane-2,2-d(2)) have been recorded and assigned using the valence empirical force field and isotopic frequency shifts. Few inactive fundamentals of adamantane-d(0) were located by means of their activity in either the low-symmetry isotopomers or the low-temperature phase. The vibrational spectrum of adamantane-d(16) had to be reinterpreted. The force field obtained from the semiempirical AM1 parametrization was scaled using the vibrational assignments for adamantane-d(0), -d(16) and-1-d(1). The two force fields were compared. Both reproduced the observed frequencies with practically the same average error of 16 cm(-1). However, the number of parameters in the scaled semiempirical force field is only nine compared with 27 of the empirical force field.