Nitromethane has been studied as a model of energetic alphatic nitro compounds. The initiation df the decomposition mechanism of nitromethane in the vicinity of its explosive decomposition pressure conditions has been studied under high static pressure at ambient temperature by Ramam spectroscopy. The vibrational modes nu(a)(NO2) and, to a lesser degree, nu(s)(NO2) show a specific behavior at the solid (II)-solid (III) 7.5 GPa transition (at ambient temperature). A comparison of the Raman spectrum of nitromethane-h(3) with new high pressure Raman spectroscopic results for nitromethane-d(3) and nitroethane allows one to characterize the physico chemical behavior of these three compounds in relation to their detonic properties.