character Upon detonation, TNT undergoes a decomposition equivalent to the reaction 2 C7H5N3O6 → 3 N2 + 5 H2 + 12 CO + 2 C plus some of the reactions + CO → + C and 2 CO → + C. The reaction is exothermic but has a high activation energy in the gas phase (~62 kcal/mol). The condensed phases (solid or liquid) show markedly lower activation energies of roughly 35 kcal/mol due to unique bimolecular decomposition routes at elevated densities. Because of the production of carbon, TNT explosions have a sooty appearance. Because TNT has an excess of carbon, explosive mixtures with oxygen-rich compounds can yield more energy per kilogram than TNT alone. During the 20th century, amatol, a mixture of TNT with ammonium nitrate was a widely used military explosive. TNT can be detonated with a high velocity initiator or by efficient concussion. For many years, TNT used to be the reference point for the Figure of Insensitivity. TNT had a rating of exactly 100 on the "F of I" scale. The reference has since been changed to a more sensitive explosive called RDX, which has an F of I rating of 80. Energy content The heat of detonation utilized by NIST to define a tonne of TNT equivalent is 1000 cal/g or 1000 kcal/kg, 4.184 MJ/kg or 4.184 GJ/ton. The energy density of TNT is used as a reference point for many other explosives, including nuclear weapons, the energy content of which is measured in equivalent kilotons (~4.184 terajoules or 4.184 TJ or 1.162 GWh) or megatons (~4.184 petajoules or 4.184 PJ or 1.162 TWh) of TNT. The heat of combustion however is 14.5 megajoules per kilogram or 14.5 MJ/kg or 4.027 kWh/kg, which requires that some of the carbon in TNT react with atmospheric oxygen, which does not occur in the initial event. For comparison, gunpowder contains 3 megajoules per kilogram, dynamite contains 7.5 megajoules per kilogram, and gasoline contains 47.2 megajoules per kilogram (though gasoline requires an oxidant, so an optimized gasoline and O2 mixture contains 10.4 megajoules per kilogram). Detection Various methods can be used to detect TNT, including optical and electrochemical sensors and explosive-sniffing dogs. In 2013, researchers from the Indian Institutes of Technology using noble-metal quantum clusters could detect TNT at the sub-zeptomolar (10−18 mol/m3) level. Safety and toxicity TNT is poisonous, and skin contact can cause skin irritation, causing the skin