LARGE-AMPLITUDE VIBRATIONS AND MICROWAVE BAND SPECTRA .2. 1-ADAMANTAMINE

The microwave spectra of 1-adamantamine, [*HI] 1-adamantamine and ['H2] 1-adamantarnine have been observed at room temperature in the frequency range 8-40GHz. The spectra consist of both F~ R-branch and F~ Q-branch bands. The pa R-branch bands of the three isotopic species appear as doublets and this is attributed to the inversion of the amine group. A simple treatment of the internal rotation and inversion in which the molecule is regarded as a symmetric rotor shows that six series of AK = +l pc Q-branch bands should be associated with the ground vibrational state. The band frequencies are shown to follow approximately the formulae v = a(2K + 1) or v = a(2K + l)+b where the constants a are the sum of the rotational constant A - B and contributions from the internal motions. The formulae are verified experimentally for ['H,]l-adarnantamine. The barrier to internal rotation in [2H,]1-adamantamine is determined to be V, = 9.0 (9) kJ mol-' [750 (70) cm-'1 and the inversion splitting to be A; = 1250 (30) MHz.