Graphic representation of the abundances of C_nH_m hydrocarbons from Table A.1. The abscissa corresponds to the number of carbon atoms in the molecule and the ordinate to the column density of each hydrocarbon. For species whose abundance has been estimated from cyano derivatives the upper and lower ranges are indicated by two green squares. For the other species the abundance is indicated by a single red square and the error is represented by a vertical black line. Abundances of the most abundant cations, according to the chemical model (see text), are indicated in magenta.