Molecular excitation temperatures. Different colours indicate different species; carbon chains and hydrocarbons are shown in blue, cyan and green and are plotted to the left on the x-axis for each source. Molecules containing the cyanide group are shown in red, orange and pink and are plotted to the right. Black stars indicate the kinetic temperatures as derived from ammonia. For each group, the molecules on the x-axis are ordered from left to right according to increasing number of atoms.