Toshikazu Arai, Hideki Yayama, and Kimitoshi Kono, Electron attachment to atomic hydrogen on the surface of liquid ⁴He: Электроны над жидким гелием, Low Temp. Phys. 34, (2008) [Fiz. Nizk. Temp. 34, 496-503, (2008)] DOI: https://doi.org/10.1063/1.2911662.