Dependence of the excitation temperature (T_ex) of the 4_1,4−3_1,3 and 5_1,5−4_1,4 transitions of ortho H₂CCC on the column density and the H₂ density, on the assumption that the kinetic temperature is 10 K. The colour scale applies to the 4_1,4−3_1,3 transition and the dashed contours to the 5_1,5−4_1,4 transition.