Left panel: time evolution of CN, C, CO, C₂, C₃, and He⁺ abundances with respect to H₂ for the fiducial model. Right panel: time evolution of the ¹²C/¹³C for CN, C, CO, C₂, and C₃ for the fiducial model. The black horizontal dashed line represents the initial ¹²C/¹³C ratio of 68. In both panels, the vertical purple solid line represents the ’early chemistry time’ as defined in the text, while the two vertical orange solid lines represent the two times (3 × 10⁴ yr, and 3 × 10⁵ yr) that we have analysed and discussed in the text.