Laser diagnostics of H- formation in a magnetic multicusp ion source

The populations of ground electronic state atomic hydrogen and ground electronic state, vibrationally, rotationally excited hydrogen molecules in a negative hydrogen ion source discharge have been measured using vacuum ultraviolet (VUV) laser absorption spectroscopy. Vibrational states up to v=8 and rotational levels as high as J=15 have been measured. The measurements have been made under a range of discharge conditions. The complete vibrational population distribution for v=8, J=1 has been obtained. The vibrational distribution appears to be thermalized and does not exhibit a plateau at the higher vibrational levels, like most models of the system. In contrast, the high rotational states are populated suprathermally. These determinations indicate that rotationally excited molecules may play an important role in the production of H/sup -/ in these sources.<>