Carbon dioxide in pollucite, a feldspathoid with ideal composition (Cs,Na)16Al16Si32O96 · nH2O

""We report a single-crystal Fourier-transform infrared (FTIR) study of a sample of pollucite from. Maine, USA. Prior to our work, the sample had been characterized by single-crystal X-ray diffraction,. neutron diffraction and electron-probe microanalysis. It is cubic Ia3¯ d, with a crystal-chemical formula. Na1.93(Cs10.48Rb0.31K0.04)S=10.83(Al14.45Si33.97)S=48.42O96·3.92H2O, and an H2O content, determined. by thermogravimetric analysis, of 1.6 wt.%. The single-crystal FTIR spectrum has a doublet of intense. bands at 3670 and 3589 cm1, which are assigned to the n3 and n1 stretching modes of the H2O. molecule, respectively. A very intense and sharp peak at 1620 cm1 is assigned to the n2 bending. vibration. In the near-infrared region there is a relatively intense peak at 5270 cm1, which is assigned. to a combination (n2 + n3) mode of H2O, and a weak but well defined doublet at 7118 and 6831 cm1,. which is assigned to the first overtones of the fundamental stretching modes. A relatively weak but. extremely sharp peak at 2348 cm1 shows that the pollucite contains CO2 molecules in structural. cavities. Mapping the sample using FTIR indicates that both H2O and CO2 are homogeneously. distributed. Secondary ion mass spectrometry yielded an average CO2 content of 0.090.02 wt.%. On. the basis of this value, we determined the integrated molar absorption coefficient for the spectroscopic. analysis of CO2 in pollucite to be eiCO2. = 11,0003000 l mol1 cm2; the linear molar absorption. coefficient for the same integration range is elCO2. = 1600500 l mol1 cm1""