Spectroscopy of mass-selected niobium trimers in argon matrices

Abstract

The absorption (scattering depletion) spectrum and Raman spectra for Nb3 in an argon matrix prepared by the mass selected ion deposition technique have been obtained. The absorption spectrum in the visible region shows three overlapping transitions, centered at 20 300 cm−1 (A), 18 800 cm−1 (B), and 17 000 cm−1 (C), respectively. Resonance Raman spectra obtained with excitation into these bands display two distinct fundamental frequencies at 227.4±2.9(e′) and 334.9±2.8(a1′) cm−1 which indicate that the ground state of the Nb3 molecule has a nearly equilateral triangular geometry (D3h). The fr (bond stretch) and frr (stretch–stretch interaction) force constants for Nb3 are determined to be 1.95 and 0.05 mdyn/Å, respectively. The Raman excitation profiles bear a strong resemblance to the triniobium absorption spectrum, but the peaks seem more closely spaced than the absorption spectrum. Both a1′ and e′ vibration are observed with the same intensity near the peak A, while the a1′ vibration dominates the profile at the peak B. Neither displays much intensity near the peak C.