A 3 4 0

Surface Science 156 (1985) 867 874 867 North-Holland, Amsterdam

S P E C T R O S C O P I C C H A R A C T E R I Z A T I O N O F P H O T O S E N S I T I V E

INTERCONVERTIBLE TRISILVER CLUSTERS IN XENON AND KRYPTON M A T R I C E S

U. K E T T L E R , P.S. B E C H T H O L D a n d W. K R A S S E R

lnstitut fi~r FestkOrperforschung, Kernforsehungsanhlge J~ilieh. 1)-5170 .ltdich. Fed. Re/). ~l" Germany

Received 20 August 1984

Three kinds of Ag 3 clusters are identified in solid Xe and Kr matrices. They can reversibly be transformed into one another by laser irradiation into the corresponding absorption bands located at 425,442, and 475 nm in Xe matrices and at 417, 423, and 448 nm in Kr matrices, respectively. Correlated laser-induced emission bands are observed at 555,659, and 760 nm in Xe matrices and at 445,485, and 563 nm in Kr matrices, respectively. The Stokes shift of these fluorescence bands shows a linear dependence with respect to the emission wavelength. Although the photosensitive clusters interconvert in times short to the accumulation time necessary, it is possible to obtain resonance Raman spectra by a dual-beam technique. The results can be interpreted in terms of a photoisomerization process.

Surface Science 156 (1985) 875 882 875 North-Holland, Amsterdam

T R A P P I N G - S I T E E F F E C T S I N R E S O N A N C E R A M A N S P E C T R A O F A g z

M O L E C U L E S I S O L A T E D I N R A R E - G A S M A T R I C E S

P.S. B E C H T H O L D , U. K E T T L E R a n d W. K R A S S E R

lnstitut ff~r Festk6rperforschung, Kernforsehungsanlage J~lich, D- 5l 70 Jgdich. Fed. Rep. of Gerrnanv Received 20 August 1984

The trapping sites of Ag 2 molecules in rare-gas matrices are characterized by their vibrational modes as measured by resonance Raman scattering. Low-energy modes that form combination bands with the Ag a stretching vibration are identified as external localized or resonant modes of the molecule. The disputed absorption band at 443 mn in argon matrices is shown to be due to Ag 2. The absorption band at 356 nm in neon matrices is correlated with a 180.8 cm 1 vibrational band. Possible lattice sites of disilver in rare-gas matrices are briefly discussed.

Surface Science 156 (1985) 883 887 North-Holland, Amsterdam

M A G N E T I C S U S C E P T I B I L I T I E S O F S M A L L P A R T I C L E S O F

M A G N E S I U M A N D B E R Y L L I U M

K. K I M U R A a n d S. B A N D O W

Instrument Center, Institute for Molecular Science, Mvodaiji, Okazaki 444, Japan

a n d

883

A341

S. S A K O

Department of Physics, Faculty of Education, Mie University, Tsu, Mie 514, Japan

Received 10 July 1984

A surface effect on the magnetic properties of very small particles is examined for two colloidal systems, particles in THF and in hexane. In the former system, two spin origins, surface impurities and volume spins, are distinguished by the power and the frequency dependence of the conduction electron spin resonance. In the latter system free from surface impurities, the magnetic susceptibili- ties exhibits a quite unusual behavior showing a decrement at low temperature. The decline of the magnetic susceptibilities both in Mg and Be small particles in the low-temperature region is discussed in relation to the quantum size effect.

888 Surface Science 156 (1985) 888-892 North-Holland, Amsterdam

S P I N - F L O P I N A N T I F E R R O M A G N E T I C M I C R O C R Y S T A L S

S t e e n M O R U P

Laboratory of Applied Physics I1, Technical University of Denmark, DK- 2800 Lyngby, Denmark Received 31 July 1984

The magnetic properties of an antiferromagnetic microcrystal with a small uncompensated magnetic moment are discussed. It is found that when an external magnetic field is applied parallel to the easy direction, the spin-flop takes place at a higher applied magnetic field than in the bulk and the transition is of second order instead of first order as observed in the bulk. It is also shown that application of the external magnetic field perpendicular to the easy direction may result in second-order spin-flop transitions at two different values of the magnetic field.

Surface Science 156 (1985) 893-898 893 North-Holland, Amsterdam

E S R O N S I L V E R C L U S T E R S I N Z E O L I T E A

P.J . G R O B E T * a n d R . A . S C H O O N H E Y D T *

Katholieke Universiteit Leuven, Laboratorium voor Oppervlaktechemie, Kardinaal Mercierlaan 92, B-3030 Leuven (Heverlee), Belgium

Received 26 July 1984

ESR results on silver cluster formation in zeolite A with different loadings are presented. Depending on the reduction degree hyperfine spectra with seveu and nine lines and two types of conduction electron spin resonance lines are detected. These signals could be assigned to the evolution in silver cluster formation in and outside the zeolite structure. Zeolites are good supports to prove the experimental evidence of the quantum size effect in small metal particles.