Fractional abundances for source B3 with a cosmic-ray ionization rate of 1 × 10⁻¹⁶ s⁻¹, a gas densityof 10⁹ cm⁻³ for a fast warm-up. All species are shown in the key with color-coded dashed horizontal lines showing the observed abundances for source B3. The thinner dashed lines indicate the upper limit for HC₃ N and the lower limit for C₂H₅CN, as they are the species that constrain the time span. The best fit time period of 3.4 kyr is shaded. The colors are coded as in Fig. 6.