During the low-temperature field evaporation of the emitter of tantalum, carried out in the presence of a small amount of hydrogen in the system, tantalum mono-, di- and trihydride ions are detected. The formation process of hydrides is explained based on the electric field-induced, localized energy states of tantalum, which combines with the field adsorbed hydrogen to produce a transition complex on the emitter surface. The complex with its low surface bond energy undergoes desorption in the high electric field applied.