¹²C/¹³C isotope ratios from C³⁴S/¹³C³⁴S, CN/¹³CN, C¹⁸O/¹³C¹⁸O, , CH⁺/¹³CH⁺, and CH/¹³CH plotted as a function of the distance from the Sun. The red symbol ⊙ indicates the ¹²C/¹³C isotope ratio of the Sun. The ¹²C/¹³C ratios directly derived from C³⁴S/¹³C³⁴S in the J = 2−1 transition with minor opacity corrections in the current work are plotted as black filled circles. The blue triangles, orange pentagons, yellow stars, green squares, and green diamonds are values determined from CN (Savage et al. 2002; Milam et al. 2005), C¹⁸O (Langer & Penzias 1990; Wouterloot & Brand 1996; Keene et al. 1998), H₂CO (Henkel et al. 1980, 1982, 1983, 1985; Yan et al. 2019), CH⁺ (Ritchey et al. 2011), and CH (Jacob et al. 2020), respectively, using state of the art distances.