ABSORPTION, RESONANCE RAMAN, AND RAMAN EXCITATION-SPECTRA OF HAFNIUM TRIMERS

We report on the optical, resonance Raman, and excitation profile spec tra of mass selected hafnium trimers in argon matrices at 14 K. The ab sorption spectrum consists of four overlapping transitions in the rang e 605-620 nm. The Raman spectrum is too complex to be attributed to a single ground state. We may explain the observed spectrum by assuming five low-lying excited states A, B, C, D, and E at 319.0, 413.4, 609.6 , 642.8 (weak), and 785.4 cm(-1), respectively. The ground (X) state s hows complex structure which may be interpreted as the result of a str ong, but linear Jahn-Teller effect. Evidence is obtained for two pseud o-rotational progressions having states of vibronic angular momentum o f j = +/- 1/2,...,+/- 7/2 based upon a'(1) normal frequencies of 142.8 and 278.1 cm(-1). This indicates a fluxional ground state with E' sym metry in the D-3h limit. No such effects are apparent in the low-lying excited states, although a'(1) modes of 143-152 cm(-1) are observed a nd in some cases geometrical information may be inferred. The A state (319.0 cm(-1)) is geometrically an equilateral triangle (D-3h symmetry ). The B state (413.4 cm(-1)) shows an a; nontotally symmetric mode no geometrical information can be obtained. The C state (609.6 cm(-1)) s hows only a nontotally symmetric mode at 116.7 cm-l, while the D state (642.8 cm(-1)) and the E state (785.4 cm(-1)) both appear to have D3h symmetry. Raman excitation profiles appear as several distinct types and correlate well with the four absorption bands at 606, 610, 615, an d 619 nm. (C) 1997 American Institute of Physics.