METHYL TORSION IN TOLUENE (H8, D8) AND NITROMETHANE (H-3, D3) IN THE POLYCRYSTALLINE STATE

The Raman spectra of toluene and nitromethane at about -150°C were observed in the region of 10-250 cm-1. In toluene-h8 two weak and sharp bands observed at 77 and 115 cm-1 were assigned to the CH3 torsion. In toluene-d8 the CD3 torsion was not observed distinctly. The assignment was confirmed by the calculation of the torsional energy levels on the basis of the C2v, symmetry by the finite element method. The potential function was assumed to be Σ1/2V n(1 -cosnβ) (n = 2, 6, and 12). The best fit was obtained when V2, V6, and F12 were 28, 99, and -42 cm -1, respectively, and further confirmed that the other structures observed at 106 and 94 cm-1 could be also assigned to the CH 3 torsion. In nitromethane-h3 or -d3 a very weak and broad band observed at 148 or 132 cm-1, respectively, was assigned to the methyl torsion. In the process of the adjustment of the potential constants it was found that V3 was important. The best fit was obtained when V3, V6, and V12 were 210, 150, and 30 cm-1, respectively. This shows that a sort of association takes place between a hydrogen atom of a molecule and an oxygen atom of the other. © 1979 American Institute of Physics.