Single-crystal Raman spectroscopy of natural paulmooreite Pb (sub 2) As (sub 2) O (sub 5) in comparison with the synthesized analog

The single-crystal Raman spectra of the natural mineral paulmooreite Pb (sub 2) As (sub 2) O (sub 5) from the Langban, Filipstad District, Varmland Province, Sweden, are presented for the first time. It is a monoclinic mineral containing an isolated [As (sub 2) O (sub 5) ] (super 4-) dimer. Unpolarized single-crystal spectra of the natural and synthetic samples compare favorably with each other and are characterized by strong bands around 186 and 140 cm (super -1) and three medium bands at 800-700 cm (super -1) . Band assignments were made based on band symmetry and spectral comparison between experimental band positions and those resulting from Hartree-Fock calculation of an isolated [As (sub 2) O (sub 5) ] (super 4-) anion complex. Spectral comparison was also made with lead arsenites such as synthetic PbAs (sub 2) O (sub 4) and Pb (sub 2) (AsO (sub 2) ) (sub 3) Cl and natural finnemanite to determine the contribution of the terminal and bridging O in paulmooreite. Bands at 760-733 cm (super -1) were assigned to terminal As-O vibrations, whereas stretches of the bridging O occur at 562 and 503 cm (super -1) . The single-crystal spectra showed good mode separation, allowing bands to be assigned a symmetry species of A (sub g) or B (sub g) .