Matrix-isolation FT-IR study of (CsBr) n and (CsI) n ( n = 1–3)

Abstract

The species present in the vapours of CsBr and CsI have been isolated in krypton and xenon matrices and were investigated by FT-IR spectroscopy in the range of 180–30 cm −1. The recorded spectra revealed the presence of substantial amounts of dimer beside the alkali halide monomers. The assignment of the bands and characterization of the fundamentals was carried out on the basis of DFT quantum chemical calculations. The applied B3P86 exchange-correlation functional in conjunction with the Stuttgart–Cologne relativistic effective core potentials and polarized triple-zeta valence basis set reproduced the accurate experimental monomer Cs–Br and Cs–I bond distances within 0.001 Å, and the harmonic stretching frequency within 1.1 cm −1. Based on calculations at this level we report reliable geometrical parameters and fundamental frequencies for the dimer and trimer species (CsBr) n and (CsI) n . Utilizing the computed data we propose the identification of the E′ asymmetric stretching mode of the trimer (CsI) 3 trapped in a Xe matrix and that of (CsBr) 3 in Kr and Xe matrices.