| Research Abstract |
(2000)
We observed the mass abundance spectra of transition metal-oxide clusters produced in a gas reactive laser vaporization cluster source, using time-of-flight mass spectrometry. We have newly found stable oxide clusters (magic number clusters). M_9O_6, M_<13>O_8 and M_<43>O_<20> (M=Fe, Co, Ni) are much more abundant than other sizes oxide clusters for Fe, Co and Ni. An ab initio calculation proposed the following structure for the M_<13>O_8 : thirteen metal atoms form one atom-centered tetragonally-distorted fcc core and the eight oxygen atoms adsorb on the tree-fold sites of the metal core. For the case of Mo and W oxides, common stable cluster Me_<14>O_<42> (Me = Mo and W) is found in TOF mass spectra. Since Mo and W belong to same VIA group, and have same stable oxide in bulk (MoO_3 and WO_3) electric configurations also have important role for the magic numbers of these oxides.
(2001)
The ab initio calculations to investigate electric configurations and stable geometric structures for magic number oxide clusters, M_9O_6, M_<13>O_8 and M_<43>O_2 (M=Fe, Co, Ni) and Me_<14>O_<42> (Me = Mo and W) , have been continued and discussed with the results of photo excitation of these magic number clusters. M_9_O_6 and M_<13>O_8 (M=Fe, Co) have similar magnetic properties, metal atoms are coupled ferromagnetically, while oxygen atoms are antiferromagnetically polarized. For the case of Ni oxide clusters, magnetic property is different from the ease of Fe and Co, i.e. antiferromagnetic couplings among the Ni atoms exist.
|
