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tokens: positions, which are greatly improved by refining PECs using experimentally measured line positions, this is seldom true for the line intensities, for which DM and TDM curves are usually best computed ab initio (Tennyson 2014 ). The line intensities, which are directly based on the ab initio DMCs, often suffer from the numerical noise, especially those from the overtone transitions (Medvedev et al. 2016 ). In order to reduce this noise, it was sufficient to apply a dipole moment cut-off of 10 −8 D to the vibrational transition matrix elements, see e.g. Yurchenko et al. ( 2018c ). When computing these matrix elements, the original ab initio X – X and A – X (T)DMCs were mapped on the duo grid using the standard cubic spline interpolation technique. The final spectroscopic model in the form of the duo input file is provided as part of the supplementary data to this paper and can be also found at www.exomol.com . This also includes our fitting set of experimental frequencies. A sample of the refinement to the data of Ramsay ( 1952 ) for the X 2 Π – A 2 Σ + system is shown in Table 2 . The Obs. − Calc. values of the fit are comparable to the actual experimental measurement uncertainty. Although these may seem from the outset to be of much lower accuracy compared to previous ExoMol line lists for non-transition metal-containing diatomics, given that in the regime of ≈30 000 cm −1 an uncertainty of 0.5 cm −1 corresponds to a resolution R of ≈60 000, which is within the realms of high-spectral resolution methods of characterizing exoplanet atmospheres (Snellen 2004 ; de Kok et al. 2014 ). For all isotopologues of SH-type ( 33 SH, 34 SH, 36 SH), we use the same empirical model (PECs, SOCs, EAMCs, SRCs, and BOBCs) developed for 32 SH. When solving the Schrödinger equation, the mass of sulphur is replaced by the nuclear mass of the corresponding isotope. For the isotopologue 32 SD, however, this approach usually leads to too large discrepancies with the experimental line positions. We have therefore refined the 32 SH model by fitting to the experimental line positions of 32 SD from the A – X band, which were taken from the same sources listed in Table 1 . Ideally, this refinement should be only applied to the BOB-correction. However, due to the lack of the experimental data on the X 2 Π state for SD, we could not build an accurate and self-consistent model without including other curves into the fit. We have therefore varied the parameters of PEC( A ), PEC ( B ), BOBC ( X ), BOBC ( A ), SRC ( X ), and SRC ( A ) by fitting to the SD line positions from Ramsay ( 1952 ), Johns Ramsay ( 1961 ), and Pathak Palmer ( 1969 ). All other curves were fixed to the those from the spectroscopic model of 32 SH, including PEC( X ), SOC ( X ), SOC( X – A ), SOC( X – B ), SOC( A – B ), EAMC( X – A ), and EAMC( A – B ). The rms error of this fit to the A – X line positions if SD is 0.4 cm −1 . The spectroscopic model for SD is included in the supplementary material as a