Abstract
Neutral excitations generated in a discharge near a sharp tungsten tip operated in either the field emission or field ionization mode in liquid helium were detected with a surface ionization detector submerged in the liquid. The measured times of flight of the neutral excitations from the tip to the detector are in excellent agreement with a model in which the neutral entities drift with the fluid which is set in motion by the force of the ion current extracted from the discharge. Times of flight as long as 30 sec were measured. These data, along with measurements reported by other workers, clearly identify the neutral excitation as an a 3Σ u + metastable helium molecule. We report a lower limit of 10 sec on the lifetime of this state.
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Mehrotra, R., Mann, E.K. & Dahm, A.J. A study of the neutral excitation current in liquid 4He above 1 K. J Low Temp Phys 36, 47–65 (1979). https://doi.org/10.1007/BF00174911
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DOI: https://doi.org/10.1007/BF00174911