The effect of polyethylene windows of standard absorption cells on the infrared spectra of vapours

Abstract

It is shown that standard absorption cells for vapors or gases which are equipped with polyethylene windows must be used with caution since the vapor of many compounds diffuses spontaneously into the polyethylene once the compound has been filled into the cell. The resulting enrichment of the compound in the polyethylene windows gives rise to spectra which are superpositions of the spectra of the molecules entrapped in the polymer and of the molecules of the vapor phase. Because the frequencies of the vibrational transitions of the molecules entrapped in the polyethylene often undergo frequency shifts (“solvent shifts”), additional, spurious bands may appear in the spectrum and/or changes in the apparent contours of the rotation—vibration branches may take place.