Absorption and Raman Spectroscopy of
Mass-Selected Scandium Tetramers in Argon Matrices

Bing Zhao, Haiyan Lu, Joseph Jules, John R. Lombardi

    To be published:  Chemical Physics Letters

Abstract

We have examined both the absorption and resonance Raman spectra of mass-selected Sc clusters, and have obtained the spectra of tetramers of Sc. Tetramers are produced in a sputtering source and mass filtered with a Wien filter, then neutralized and deposited in an Ar matrix at low temperatures. The absorption spectrum indicates several new optical transitions at 350, 451, 538, and 563nm. Raman resonances were excited at 488 nm with transitions at 222 cm-1, 166 cm-1, and 103 cm-1. These indicate a tetramer geometry that is likely tetrahedral (Td), and we assign them to a singly degenerate totally symmetric stretch n1(a1), a triply degenerate mode n2(t) and a doubly degenerate n3(e) mode respectively. We examine the variation of the force constants of the small scandium clusters as a function of cluster size.
 

          Table : Force constants (mdyne/Å) for small clusters of Sc and Ta.
 

Clusters
Scandium
 k(n)/k(2)
Tantalum
 k(n)/k(2)
Dimer
0.756
  
 4.80 
  
 Trimer 
 0.539
 0.71
 2.25
 0.47
 Tetramer 
 0.318 
 0.42 
 1.89
 0.39

Figure. Resonance Raman spectrum of scandium deposited at a mass-to-charge ratio of 90 in an argon matrix at 16K. The excitation wavelength is the 488 nm line of the argon ion laser at a power of 80 mW. The line at 327 cm-1 is due to the CaF2 substrate and is used as a calibration mark.


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