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We studied the line emission from CH3CN and its deuterated isotopologueCH$_2$DCN towards the prototypical Class I object SVS13-A, where thedeuteration of a large number of species has already been reported. Our goal isto measure the CH$_3$CN deuteration in a Class I protostar, for the first time,in order to constrain the CH$_3$CN formation pathways and the chemicalevolution from the early prestellar core and Class 0 to the evolved Class Istages. We imaged CH2DCN towards SVS13-A using the IRAM NOEMA interferometer at3mm in the context of the Large Program SOLIS (with a spatial resolution of1.8"x1.2"). The NOEMA images have been complemented by the CH$_3$CN andCH$_2$DCN spectra collected by the IRAM-30m Large Program ASAI, that providedan unbiased spectral survey at 3mm, 2mm, and 1.3mm. The observed line emissionhas been analysed using LTE and non-LTE LVG approaches. The NOEMA/SOLIS imagesof CH2DCN show that this species emits in an unresolved area centered towardsthe SVS13-A continuum emission peak, suggesting that methyl cyanide and itsisotopologues are associated with the hot corino of SVS13-A, previously imagedvia other iCOMs. In addition, we detected 41 and 11 ASAI transitions ofCH$_3$CN and CH2DCN, respectively, which cover upper level energies (Eup) from13 to 442 K and from 18 K to 200 K, respectively. The derived [CH2DCN]/[CH3CN]ratio is $\sim$9\%. This value is consistent with those measured towardsprestellar cores and a factor 2-3 higher than those measured in Class 0protostars. Contrarily to what expected for other molecular species, the CH3CNdeuteration does not show a decrease in SVS13-A with respect to measurements inyounger prestellar cores and Class 0 protostars. Finally, we discuss why ournew results suggest that CH3CN was likely synthesised via gas-phase reactionsand frozen onto the dust grain mantles during the cold prestellar phase.

CH$_3$CN deuteration in the SVS13-A Class I hot-corino. SOLIS XV