Using partially deuterated isotopomers lowers the symmetry of the system, thus allowing new rotamers to be spectroscopically active and giving rise to band splittings.77,78 Calculated (harmonic and anharmonic) frequencies for the fundamentals of the non-, mono- and di-deuterated isotopomers of nitromethane are compiled in Tables 2, 3 and 4, respectively. Experimental frequencies77,79–81 are also given for comparison.