Raman spectrum of mass-selected terbium dimers in argon matrixes

We report on the absorption, resonance Raman, and Raman excitation profile spectra of mass-selected terbium dimers in argon matrixes. An absorption ba nd found between 620 and 680 nm was assigned to terbium dimers. The Raman e xcitation profile of dimer frequencies resembles closely this absorption sp ectrum. Unlike other lanthanide dimers, resonance Raman spectra of terbium dimer, obtained by excitation into this region with tunable dye laser radia tion, gives two progressions with one up to 7 Stokes transitions, and the o ther up to 4 transitions. We interpret these to represent two distinct elec tronic states X and A. For the ground (X) state, we obtain omega (e) = 137. 6 +/- 0.4 cm(-1) with omega (e)x(e) = 0.31 +/- 0.05 cm(-1), leading to a sp ectroscopic dissociation energy of 1.9 +/- 0.3 eV, force constant k(e) = 0. 88 +/- 0.01 mdyn/Angstrom. The first electronic (A) state has an origin at 313.9 cm(-1) with a progression in omega (e) = 136.3 +/- 0.2 cm(-1) and ome ga (e)x(e) = 0.14 +/- 0.05 cm(-1), leading to an excited-state spectroscopi c dissociation energy of 4.1 +/- 1.2 eV.