吉田 弘幸

Photoelectron spectra of vanadium cluster anions, V-n(-) (3 less than or equal to n less than or equal to 100), were measured at a photon energy of 3.49 eV (355 nm) by using a magnetic-bottle-type photoelectron spectrometer. The electronic density-of-state profiles and the photoelectron spectra of V-4(-) and V-3(-) were calculated by the spin-polarized DV (discrete variational)-X alpha method for several plausible geometrical structures, The most plausible structure was determined so that the calculated photoelectron spectrum based on this structure well reproduces the observed one. The calculation showed that V-4(-) has a square planar geometrical structure and a charge distribution of D-4h symmetry. On the other hand, V-3(-) was found to possess an equilateral triangle geometrical structure, but C-2v symmetry for the charge distribution. The electronic states in the vicinity of the Fermi energy were found to consist of 3d atomic orbitals. The population differences between the minority and the majority spins per atom turned out to be 4.6 and 1.7 for V-4(-) and V-3(-), respectively. The result implies that the d-electron spins are coupled ferromagnetically in these cluster anions. In addition, the size-dependence of the electron affinity of V-n was explained by a spherical conducting droplet model in the n greater than or similar to 9 range. (C) 1997 American Institute of Physics.

The photoelectron spectra of Co-n(-) (3 less than or equal to n less than or equal to 70), ComN- and ComO- (3 less than or equal to m less than or equal to 6) were measured by a XeCl excimer laser (4.025 eV). Also the reactivities of Co-n(-) with O-2 and CO were measured. A clear distinction between the cluster size of n less than or equal to 6 and that of n greater than or equal to 7 was observed both in the photoelectron spectra and in the reactivities. (i) In the size range above n = 7, the electron affinities of the cobalt clusters determined by the photoelectron spectra are linearly dependent on the reciprocal of the cluster radius, but below this size they deviate from this relation. (ii) The reactivity of Co-n(-) with O-2 in the size range below n = 6 is higher than that above n = 7. However, the reactivity with CO in the size range below n = 6 is extremely lower than that above n = 7. These findings suggest that a transition of electronic structure in size dependence, which is correlated with the reactivity, occurs at n similar or equal to 7.

Photoelectron spectra of (CO2)nH2O- (2 less-than-or-equal-to n less-than-or-equal-to 8) and (CO2)n(H2O)2- (1 less-than-or-equal-to n less-than-or-equal-to 2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO2)nH2O-, the VDE-n plots exhibit a sharp discontinuity between n = 3 and 4; the VDE value is almost-equal-to 3.5 eV at n = 3, while it drops down abruptly to 2.59 eV at n = 4. This discontinuity in VDE is ascribed to ''core switching'' at n = 4; a C2O4- dimer anion forms the core of (CO2)nH2O- for n less-than-or-equal-to 3, while a monomer CO2- is the core for n greater-than-or-equal-to 4. The (CO2)2(H2O)2- ion has a VDE of 2.33 eV, indicating the presence of a CO2- monomer core in the binary clusters containing two H2O molecules.