Resonance Raman spectroscopy of mass selected chromium trimers in an argonmatrix

The resonance Raman spectra of mass-selected chromium trimers (Cr-3) in arg on matrixes have been obtained. Five resonance Raman transitions were obser ved between 450 and 690 nm. Four of them are assigned to a totally symmetri c (a(1)') vibrational progression, from which we obtain a ground-state harm onic frequency of omega (e) = 432.2 cm(-1) with omega (e)x(e) = 16.3 cm(-1) . The other Raman line, observed at 302.0 cm(-1), is assigned to the degene rate bending motion nu (2)(e') of the triatomic metal cluster. The geometry of the ground state is that of an equilateral triangle (D-3h). These resul ts provide a value of the stretching force constant of k(e) = 1.91 mdyne/An gstrom and a spectroscopic atomization energy of 0.36 eV.