Lyman-α revisited

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Abstract
The cross-section for excitation of Lyman- alpha radiation following electron impact of H2 has been measured at 100 eV incident energy. The data were made absolute by comparison with the signal obtained from electron impact on H at the same energy making use of the Long, Cox and Smith value (1968) for this cross-section. Identical excitation and detection geometries were used, thus automatically removing many possible sources of systematic error. The value obtained, 7.13+or-0.59*10-18 cm2, is 42% lower than the earlier measurement of Mumma and Zipf (1971) and is in good agreement with very recent measurements obtained using less direct calibration techniques. The accuracy of the present measurement is a considerable improvement over most previous measurements.