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Aims: To trace the radial and vertical spatial distribution of H2CS, a keyspecies of the S-bearing chemistry, in protoplanetary disks. To analyse theobserved distributions in light of the H2CS binding energy, in order to discussthe role of thermal desorption in enriching the gas disk component. Methods: Inthe context of the ALMA chemical survey of Disk-Outflow sources in the Taurusstar forming region (ALMA-DOT), we observed five Class I or early Class IIsources with the o-H2CS(7_1,6-6_1,5) line on a 40 au scale. We estimated thebinding energy (BEs) of H2CS using quantum mechanical calculations, for thefirst time, for an extended, periodic, crystalline ice. Results: We imaged H2CSin two rotating molecular rings in the HL Tau and IRAS04302+2247 disks. Theouter radii are about 140 au (HL Tau), and 115 au (IRAS 04302+2247). Theedge-on geometry of IRAS 04302+2247 reveals that H2CS emission peaks, at radiiof 60-115 au, at z = +- 50 au from the equatorial plane. The column densitiesare about 10^14 cm^-2. For HL Tau, we derive, for the first time, the[H2CS]/[H] abundance in a protoplanetary disk (about 10^-14). The BEs of H2CScomputed for extended crystalline ice and amorphous ices is 4258 K and3000-4600 K, respectively, implying a thermal evaporation where dusttemperature is larger than 50-80 K. Conclusions: H2CS traces the so-called warmmolecular layer, a region previously sampled using CS, and H2CO.Thioformaldehyde peaks closer to the protostar than H2CO and CS, plausibly dueto the relatively high-excitation level of observed 7_1,6-6_1,5 line (60 K).The H2CS BEs implies that thermal desorption dominates in thin, au-sized, innerand/or upper disk layers, indicating that the observed H2CS emitting up toradii larger than 100 au is likely injected in the gas due to non-thermalprocesses.

astronomy and astrophysics

ALMA chemical survey of disk-outflow sources in Taurus (ALMA-DOT). IV.  Thioformaldehyde (H$_2$CS) in protoplanetary disks: spatial distributions and  binding energies