Direct isotopic ratios derived in L483 (see Table 2) are compared with local ISM values. Lower limits are indicated in green. In the case of c-HCC¹³CH, the c-C₃H₂/c-HCC¹³CH ratio is multiplied by two to account for the enhanced probability of substitution of either of the two equivalent carbon atoms of c-C₃H₂ (see Table 2). This way, the plotted value can be directly compared with the ¹²C/¹³C ratio in the local ISM. Isotopic ratios representative of the local ISM are indicated by red horizontal rectangles and are taken as ¹²C/¹³C = 59–76, ¹⁴N/¹⁵N = 237–450, ¹⁶O/¹⁸O = 557 ± 30, ¹⁶O/¹⁷O = 2317 ± 134, ³²S/³⁴S = 24.4 ± 5.0, ³²S/³³S = 153 ± 40 (see text in Sect. 4.5).