Integral absorption coefficients of C-H stretching bands in IR spectra of ethane adsorbed by cationic forms of Y zeolite.

An attempt to measure absolute intensities of IR C−H stretching bands of ethane specifically adsorbed by Na+, Ca2+, or Mg2+ cations in Y zeolite was carried out via simultaneous transmission IR and volumetric measurements at very low pressures using self-supporting wafers. For wafers with a thickness of 7−9 mg/cm2 quantitative measurements of absorption coefficients of C−H stretching bands were possible. More pronounced shifts of C−H bands toward lower frequencies indicated that the perturbation of the corresponding bonds in ethane upon adsorption by the bivalent Ca2+ or Mg2+ ions was much stronger than by the monovalent Na+ ions. In addition, the integral extinction coefficient of the C−H stretching bands of ethane adsorbed by Na+ ions was only about 53% of that of gas-phase ethane. For adsorption on the bivalent Ca2+ or Mg2+ ions the coefficients exceeded those of the free ethane molecule, indicating strong polarization of the C−H bonds during the vibration. Bands representing the fully symmetric C−H st...