Dimethyl(trifluoromethylthio)arsine
Dimethyl(trifluoromethylthio)arsine is an arsenical compound developed by the United States military chemical weapon research program, which is described as "one of the most potent lung irritants known."
Source: Wikipedia — Dimethyl(trifluoromethylthio)arsine (CC BY-SA 4.0)