1. Afrosimov V V, Basalaev A A, Leiko G A and Panev M N, 1978, Sov Phys JETP 47: 837.
2. Afrosimov V V, Leiko G A, Mamev Yu A and Panev M N, 1975, ibid 40: 661.
3. Aitken K L, Harrison M F A and Rundel R D, 1971, J Phys B 4: 1189.
4. Angel G C, Dunn K F, Neill P A and Gilbody H B, 1980, J Phys B 13: L391.
5. Angel G C, Dunn K F, Sewell E C and Gilbody H B, 1978a, J Phys B 11: L49.