The effect of roughness changes and the effect of the angle between the fiber direction and the incident light were studied. The DRIFT spectra of several wood species were recorded at different angles between the fiber direction and the projection of the incident light on the surface. After measuring the IR spectra, the surface of the sample was graded with sandpaper grit 600 and 120, respectively. The IR measurement was repeated after all surface modifications. Spectral intensities were calculated in K-M units. It was confirmed that the DRIFT technique is a convenient way to obtain valuable IR spectra of solid wood surfaces. To gain reproducible DRIFT spectra of wood, the surface roughness, the anatomical position of the surface, and the angle between the fiber direction and the incident IR beam must be kept constant. By using sandpaper for surface preparation, the direction dependence of the DRIFT spectra was diminished.
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