Reorientation motions of PF 6 -ions in solid KPF 6 and RbPF 6 observed by NMR pulse method - Niemelä, Lasse; Niemelä, Matti; Tuohi, Jukka (Suomalainen Tiedeakatemia, Helsinki: Annales Academiae Scientiarum Fennicae / A / 6, 1972)