We report on the absorption, resonance Raman, and Raman excitation profile spectra of mass selected lutetium dimersin argon matrices. Two.broad absorption regions were found between 415 and 545 nfi with peaks at418, 433, 452,472,505,540 nm, and between 635 and 660nmwith peaks at 640 and 652 nm. ResbnanceRaman spectra were obtained by excitation into one of these regions with the visible light of an Ar ion laser between 458 and 514 nm. Two progressions were assigned to lutetium dimmers. We interpret them to represent two distinct electronic states: A grotind-state X and an excited state A. For the ground (X) state, w~ obtain We= 121.6~0.8cm-l with WeXe =0.16::!:0.10cm-l, leading to a spectroscopic dissociation ene;gy of 2.9::!: 1.8eV, and force constant ke=0:76::!: 0.01 mdyne/A.. The lowest excited electronic state (A) has an origin at 210,7 cm -1 and almost identical vibrational parameters. C()fuparison of spectroscopic properties of lanthanide dimmers is disc.ussed, and evidence is presented that lutetium should occupy the position normally given to lanthanum in the periodic table.
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