Electronic and vibrational spectra of gaspeite
Reddy, B.J.; Frost, R.L.
published: Nov 29, 2004
Visible, near-infrared, IR and Raman spectra of magnesian gaspeite are presented. Nickel ion is the main source of the electronic bands as it is the principal component in the mineral where as the bands in IR and Raman spectra are due to the vibrational processes in the carbonate ion as an entity. The combination of electronic absorption and vibrational spectra (including near-infrared, FTIR and Raman) of magnesian gaspeite are explained in terms of the cation co-ordination and the behaviour of CO32 anion in the NiMg carbonate. The electronic absorption spectrum consists of three broad and intense bands at 8130, 13160 and 22730 cm1 due to spin-allowed transitions and two weak bands at 20410 and 30300 cm1 are assigned to spin-forbidden transitions of Ni2+ in an octahedral symmetry. The crystal field parameters evaluated from the observed bands are Dq = 810; B = 800 and C = 3200 cm1. The two bands in the near-infrared spectrum at 4330 and 5130 cm1 are overtone and combination of CO32 vibrational modes. For the carbonate group, infrared bands are observed at 1020 cm1(ν1 ), 870 cm1 (ν2), 1418 cm1 (ν3) and 750 cm1 (ν4), of whichν3, the asymmetric stretching mode is most intense. Three well resolved Raman bands at 1571, 1088 and 331 cm1 are assigned to ν3, ν1 and MO stretching vibrations.