Local constraints on alcohol--thioalcohol analogs in G35.2N

The chemistry of sulfur-bearing complex organic molecules in dense star-forming environments remains uncertain, partly because the dominant sulfur reservoirs in dense gas and ices are poorly identified. Alcohol--thioalcohol pairs allow direct comparisons of structurally related O- and S-bearing molecules. We present ALMA Band 6 observations of CH 3 OH/CH 3 SH and C 2 H 5 OH/C 2 H 5 SH toward three spectral-extraction positions (MM3-pos, MM4-pos, and MM5-pos) in the MM3--MM5 region of G35.2N. Local thermodynamic equilibrium modeling yields column densities and abundance ratios. CH 3 OH column densities were inferred from 13 CH 3 OH assuming 12 C/ 13 C = 50 to mitigate optical-depth effects. CH 3 OH, CH 3 SH, and C 2 H 5 OH are robustly constrained at all three positions; C 2 H 5 SH is robustly constrained at MM3-pos and MM5-pos but remains tentative at MM4-pos. The corresponding adopted column-density ranges are (1.8-2.7) times10 18, (1.7-2.6) times10 16, (5.7-8.5) times10 16, and (2.4-4.6) times10 15 cm-2. The CH 3 OH/C 2 H 5 OH and CH 3 OH/CH 3 SH ratios are consistent across the positions within uncertainties, with nominal values of 31--32 and 100--110, respectively. Comparisons with chemically rich sources and warm-up chemical models show that CH 3 OH/C 2 H 5 OH lies within the range measured elsewhere, whereas CH 3 OH/CH 3 SH exhibits greater source-to-source variation. The ethyl-level O/S comparison remains less certain because many literature C 2 H 5 SH measurements provide only lower limits. CH 3 OH/CH 3 SH is thus the best-constrained O/S alcohol--thioalcohol ratio in these data and provides an empirical probe of source-dependent sulfur-bearing organic chemistry. More sensitive C 2 H 5 SH observations are needed to test C 2 H 5 OH/C 2 H 5 SH.