Thermo-optical determination of vapor pressures of TNT and RDX nanofilms

Accurate thermodynamic parameters of thin films of explosives are important for understanding their behavior in the nanometer scale as well as in standoff detection. Using UV-absorbance spectroscopy technique, accurate thermodynamic parameters such as activation energies of sublimation, sublimation rates, and vapor pressures of the explosives cyclotrimethylenetrinitramine (RDX) and 2,4,6-trinitrotoluene (TNT) were determined. The values of these parameters are in excellent agreement with those reported using traditional experiments based on gravimetry. In terms of the Clapeyron equation, the dependence of RDX and TNT vapor pressures on temperature can be described by the relations LnP (Pa) = 39.6 - 15459/T (K) and LnP (Pa) = 34.9 - 12058/T (K), respectively. Heats of sublimation of RDX and TNT were also determined to be 128 kJ/mol and 100.2 kJ/mol, respectively.