used as a catalyst in the hydrogenation of a few organic compounds the metal can be used in ion propulsion systems. Although not usable in the earth's atmosphere, 1 kg of caesium in outer space could propel a vehicle 140 times as far as the burning of the same amount of any known liquid or solid. It is more efficient than rubidium. used in atomic clocks because of its high oxygen affinity, the metal is used as a "getter" in electron tubes used in photoelectric cells and vacuum tubes IR lamps