1. A. G. Khrapak, W. F. Schmidt, and E. Illenberger, in Electronic Excitations in Liquid Rare Gases, edited by W. F. Schmidt and E. Illenberger (American Scientific Publishers, Stevenson Ranch, 2005), p. 239.
2. Electrons in Liquid Helium
3. Positive Impurity Ions in He II
4. Impurity ions in liquid helium