Abstract
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 provide a direct basis for comparing the abundance behavior of structurally related O- and S-bearing molecules. We present ALMA Band 6 observations of G35.2N and investigate the alcohol–thioalcohol pairs CH
3
OH/CH
3
SH and C
2
H
5
OH/C
2
H
5
SH toward three selected spectral-extraction positions, MM3-pos, MM4-pos, and MM5-pos, in the MM3–MM5 region. Local thermodynamic equilibrium spectral modeling was used to derive molecular column densities and abundance ratios. The CH
3
OH column density was derived from
13
CH
3
OH by adopting
12
C/
13
C = 50, because the main isotopologue is affected by optical-depth effects. Robust column-density constraints were obtained for CH
3
OH, CH
3
SH, and C
2
H
5
OH at all three positions. C
2
H
5
SH was robustly constrained toward MM3-pos and MM5-pos but remains tentative toward MM4-pos. The adopted column densities vary moderately across the three positions, with ranges of (1.8-2.7) × 10
18
cm
−2
for CH
3
OH, (1.7-2.6) × 10
16
cm
−2
for CH
3
SH, (5.7-8.5) × 10
16
cm
−2
for C
2
H
5
OH, and (2.4-4.6) × 10
15
cm
−2
for C
2
H
5
SH. Within the adopted uncertainties, the CH
3
OH/C
2
H
5
OH and CH
3
OH/CH
3
SH ratios are consistent across MM3-pos, MM4-pos, and MM5-pos, with nominal values of 31–32 and 100–110, respectively. Comparison with other chemically rich sources and warm-up chemical models shows that the CH
3
OH/C
2
H
5
OH ratio in G35.2N lies within the range measured in other sources, whereas CH
3
OH/CH
3
SH shows a larger 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 therefore the best-constrained O/S alcohol–thioalcohol analog ratio in the present data and provides a useful empirical probe of source-dependent sulfur-bearing organic chemistry, while higher-sensitivity C
2
H
5
SH observations are needed to test the C
2
H
5
OH/C
2
H
5
SH ratio.