ARE THE INTEGRATED ABSORPTION-COEFFICIENTS TEMPERATURE-DEPENDENT - FT-NIR STUDY OF THE 1ST OVERTONE OF THE OH STRETCHING MODE OF OCTANOIC-ACID

The integrated molar absorption coefficients of the first overtone of an OH stretching mode of free octanoic acid were determined through a series of FT-NIR measurements in a CCl4 solution at different temperatures. A few methods of calculation of the molar absorption coefficient were applied; the results were compared and discussed. It was shown that not all of the methods can be applied for the calculation if the plot of Beer's law does not pass through the origin. The results clearly show that the integrated molar absorption coefficient is strongly temperature dependent; its value increases approximately 0.6 dm3 mol-1 cm-1 per one degree and the use of a constant value of the coefficient through a temperature range may lead to significant errors.