Raman spectra of rhodium trimers in argon matrices

Resonance Raman spectra of rhodium trimers (Rh3) in argon matrices have been obtained for the first time. Our samples are prepared by neutralizing a mass-filtered beam of trimer ions. Although the absorption spectrum of our optically thin samples failed to show any obvious transitions, a rich Raman spectrum was found for laser excitation wavelengths between 545 nm and 593 nm. Three fundamentals, corresponding to normal modes of a bent (C2v) molecule can be assigned with up to four overtones in the symmetric stretch. Using standard techniques, we obtained for this mode ve5322.4(6) cm , with vexe50.49(10) cm . The resulting stretching force constant is ke 52.1060.01 mdyn/Å. Assuming a Morse potential governs the symmetric stretching normal coordinate, we obtain an atomization energy of De56.661.4 eV. The asymmetric stretch and bend are found at 259 cm and 247.9~8! cm, respectively. A line at 400 cm is observed, which does not fit the normal mode scheme of the ground state. This is assigned as the origin of a low lying electronic state. © 2000 American Institute of Physics. @S0021-9606~00!00941-7#