Spectroscopy
of Mass-selected Transition Metal Clusters
    
   
John R. Lombardi and Derek M. Lindsay
   
 
Transition metal clusters are produced in an ultra high vacuum chamber by
      sputtering a metal target with high energy agron ions. The ionized clusters are
      mass selected by passing through a Wien filter. The selected cluster is then 
      neutralized and deposited on a substrate at 14K in a rare gas matrix. We then
      may study absorption, fluorescence and resonance Raman spectra. Systematic
      study of Raman spectra of transition metal dimers has resulted in filling in the 
      periodic table with measured force constants (see below).  We have also
      examined the Raman spectra of several trimers and two tetramers (Ta4 and Sc4). 
We have also recently published a review article in Chemical Reviews, 102
2431 (2002). To download in pdf formate click here. For more information, 
click on the highlighted metal in the periodic table.
 
 

             CCNY  CLUSTER  DEPOSITION  APPARATUS

             Metal cluster ions are produced by sputtering, using (typically) a 10 mA
             beam of 20 KeV rare gas ions. The cluster beam is bent by 10 degrees in
             order to separate neutral particles. The cluster ions generated are extracted,
             and mass selected using a Wien filter.  The mass selected cluster ions are
             thereafter codeposited with Kr or Ar onto a cold (10-20K) CaF2 window.

             Cluster ions are transported, at relatively high energies, to a Faraday-type
             cage which surrounds a matrix target. By biasing the cage at a positive
             voltage, the ions may be directly decelerated before landing. Electrons,
             produced at the same potential as the Faraday cage, neutralize the ions.
             This combination of ions and electrons defines, in a self regulating manner,
             the (positive or negative) potential of the matrix surface.

             The matrix samples are detected by resonance Raman, fluorescence emission and
             excitation spectroscopy. The latter are recorded either as "total excitation"
             spectra (high-pass filter + PMT), or by using a monochromator to detect
             only the emission characteristic of a particular species.
 

       TM  HOMONUCLEAR  MOLECULAR  FORCE CONSTANTS

           Dimer Force Constants
           Trimer Force Constants
           Tetramers (Tantalum and Scandium
 

       TRANSITION  METAL (TM)  MASS  SPECTRA

           Early Transition Metals
           Late Transition Metals
 


  
Experimental Force Constants (mdyne/Å)
 for Transition Metal Dimers
3 4 5 6 7 8 9 10 11
Sc
0.76
Ti
2.35
V
4.33
Cr
3.54
Mn
.094
Fe
1.48
Co
1.53
Ni
1.16
Cu
1.33
Y
0.89
Zr
2.51
Nb
4.84
Mo
6.33
Tc Ru
3.59
Rh
2.44
Pd
1.38
Ag
1.18
Lu
0.76
Hf
1.63
Ta
4.80
W
6.14
Re
6.26
Os Ir Pt
2.84
Au
2.12

Lanthanide

La
2.28
Ce
2.48
Pr
2.49
Nd
0.93
Pm
Sm
Eu
Gd
0.89
Tb
0.88
Dy
Ho
Er
Tm
Yb
Lu
0.76

 
Experimental Force Constants (mdyne/Å)
for Transition Metal Trimers
3 4 5 6 7 8 9 10 11
Sc
0.54
Ti V
2.21
Cr
1.91 
Mn
0.37
Fe
0.68
Co Ni
0.62
Cu
.91/.66
Y Zr
1.19
Nb
2.05
Mo
2.82
Tc Ru
1.86
Rh
2.10
Pd Ag
0.55
Lu Hf
0.72
Ta
2.25
W Re Os Ir Pt
1.93
Au
1.25

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