Matrix isolation study of ' " Eu atoms and molecules ?

Matrix isolation techniques have been used in conjunction with Mossbauer spectroscopy to study europium atoms and clusters in solid argon. The measured isomer shift for Eu' monomers in argon was -6.1 mms-'. A value of 13 i: 2 lO-'fm* for the change in the mean square radius (A(?)) was calculated from the isomer shifts of Eu' and EuZ+S04. It was observed that the electron density at the lslEu nucleus decreases in going from the monomer to larger clusters (multimers like E u ~ , EUJ , . .). The Mossabuer spectrum of Eun shows the presence of a hyperfine magnetic field with a value equal to the one observed for free atoms. A large quadrupole splitting was observed for Euz. The hyperfine magnetic field for larger europium clusters was around 231 kOe. The magnetic hyperfine field at the lslEu nucleus for a 71 at. % europium in argon sample was essentiallyidentical to the one observed for metallic europium at 4 . 2 K .