Absorption, resonance Raman, and Raman excitation spectra of hafnium trimers

Abstract

We report on the optical, resonance Raman, and excitation profile spectra of mass selected hafnium trimers in argon matrices at 14 K. The absorption spectrum consists of four overlapping transitions in the range 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 shows complex structure which may be interpreted as the result of a strong, but linear Jahn–Teller effect. Evidence is obtained for two pseudo-rotational progressions having states of vibronic angular momentum of j=±1/2,…,±7/2 based upon a1′ normal frequencies of 142.8 and 278.1 cm−1. This indicates a fluxional ground state with E symmetry in the D3h limit. No such effects are apparent in the low-lying excited states, although a1′ modes of 143–152 cm−1 are observed and in some cases geometrical information may be inferred. The A state (319.0 cm−1) is geometrically an equilateral triangle (D3h symmetry). The B state (413.4 cm−1) shows an a1′ vibration, but without an observed nontotally symmetric mode no geometrical information can be obtained. The C state (609.6 cm−1) shows only a nontotally symmetric mode at 116.7 cm−1, 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, and 619 nm.