The evaporation of a dicationic ionic liquid, 1,3-bis(3-methylimidazolium-1-yl)propane bis(trifluoromethanesulfonyl)amide ([C-3(MIm) (2+)(2)][Tf2N-](2)), was studied by Knudsen effusion mass spectrometry. Its evaporation is accompanied by a partial thermal decomposition producing monocationic ionic liquids, 1,3-dimethylimidazolium and 1-(2propenyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amides, as volatile products. This decomposition does not affect the vaporization characteristics of [C-3(MIm)(2)(2+)][Tf2N-](2), which were established to be as follows. The vaporization enthalpy (550 K) is equal to (155.5 +/- 3.2) kj.mol(-1); the saturated vapor pressure is described by the equation ln(p/Pa) = -(18699 +/- 381)/ (T/K) + (30.21 +/- 0.82) in the range of 508-583 K. 1,3-Bis(3-methylimidazolium-1-yl)propane bis(trifluoromethanesulfonyl)amide is the first dicationic ionic liquid, the vaporization charactenstics of which were determined with an acceptable accuracy.