Infrared spectra of crystalline polysaccharides. IV. The use of inclined incidence in the study of oriented films

The infrared spectra (tilting spectra) obtained with the incident beam inclined to oriented films are discussed. Various experimental settings for obtaining the tilting spectra are studied. It is pointed out that quantitative interpretations (to determine the direction of the transition moment of a normal mode) of the tilting spectra are not possible at present. Qualitative interpretations, however, are usually possible. The tilting spectrum of a uniaxially oriented film of chitin crysallites at various settings is presented for the purpose of demonstrating different tilting effects. The tilting spectra of 101 and 101 uniplanarly oriented films of cellulose I materials and of doubly oriented films of cellulose I and cellulose II crystallites are presented. A number of interesting tilting effects in these spectra are discussed in terms of crystal structure.