Top panels: calculated radial distributions of abundances expressed as number of particles per unit volume. Curves have been arbitrarily scaled in the y-axis for display. Bottom panels: comparison between calculated (neglecting and including infrared pumping) and observed radial distributions of the emission at velocities around V_LSR = V_sys for the lines of C₂H, C₄H, and C₆H (left), and CN, C₃N, HC₃N, and HC₅N (right) plotted in Fig. 1. The observed brightness distributions are those previously shown in Fig. 4. Curves have been arbitrarily scaled and shifted along the y-axis for display.