Production of H− from heated SrH2 powder and from H2 introduced onto the powder

The currents (J− and I−) of thermal electron (e−) and ion (H−) desorbed from heated powdery SrH2 were simultaneously measured by mass spectrometry as a function of the sample temperature, introduced H2 gas pressure or time elapsing after increasing temperature, introducing H2 or stopping the introduction. Analysis of the data thus obtained yields the notable results as follows. (1) Above ∼800 K, those active spots (Sr) with low work function (φ) is created by such a thermal decomposition as SrH2→Sr+H2. (2) From the spots, not only e− but also H− is desorbed even without introducing H2. (3) By introducing H2 up to ∼5×10−4 Torr, φ is increased by up to ∼0.3 eV according to a deactivation reaction (Sr+H2→SrH2). (4) By this increase, J− is decreased to less than 1/10 but I− is increased up to ∼2.4 times. In conclusion, H− is thermally produced not only from the H constituent of powdery SrH2 kept above ∼800 K but also from the H2 introduced onto the hydride, in spite of low electron affinity of hydrogen.