In a chemical ionization source with CH4/N2O, carbon disulfide (CS2) yields its radical anion by electron capture and CHS2- by hydride attachment, By combining tandem mass spectrometric experiments and theoretical ab initio calculations, we demonstrate that hydride attachment can yield either thioformate anion or thiohydroxythiocarbonyl carbanion without interconversion. The thioformate anion reacts with neutral at CS2 carbon, whereas the syn thiohydroxythiocarbonyl carbanion attacks at the sulfur site to ultimately form HSCS2- and CS species.