Nitro group asymmetric stretching mode lifetimes of molecules used in energetic materials

Picosecond infrared pump–probe measurements of the vibrational relaxation of the nitro (NO2) functional group asymmetric stretch (∼1580 cm−1) of several molecules used in energetic materials, TNAZ, RDX, HMX, and CL-20 (abbreviations defined in text), and nitromethane, are presented. In addition, a temperature-dependent study was performed between 50 and 298 K on TNAZ. All of the lifetimes fall in the range of 2–6 ps with the exception of nitromethane, which has a lifetime of 16 ps. The temperature dependence of TNAZ is flat and solvent independent, suggesting an intra-molecular relaxation pathway that does not involve low-frequency modes.