红外吸收峰的强度与反常吸收现象

Absorbance of Infrared Bands and Anomalous Absorption

红外光谱测量有时需要在强的背景信号下得到弱的样品吸收峰,如在大量溶剂中测量溶质的红外光谱。理论上,只要某一组分在背景样品和待测样品的含量(分子个数)完全一致,则该组分的光谱信号就不会出现在最终的红外光谱图上。而实际测量时结果并非总如此。本文在测量聚苯乙烯及硬脂酸的"基线"时发现,在样品吸收较强的峰位(吸光度A>1.0)会出现反常吸收。反常吸收的吸光度或正或负,明显超过随机噪音水准。而在样品峰吸收较弱(A<1.0)的区域,则不会出现反常吸收。本文对反常吸收出现的原因,该现象对光谱测量的影响,以及测量时如何避免反常吸收进行了有益的探讨。

To remove the background signals from an IR spectrum is very useful and ideally all that remain in an IR spectrum are the desired absorption bands.Unfortunately,the removal of background bands is not always completely effective.In the present paper,an absorbance spectrum was obtained by scanning the same sample（polystyrene film or stearic acid KBr disc） both in background and sample single-beam measurements.It was found that a series of residual spikes appear in the strong absorption regions.The residuals are significantly different from that of random noise.There should be a nearly straight line according to theory analysis while spikes appear.Therefore those spikes are called anomalous absorption.The experimental results indicate that anomalous absorption is related to the absorbance of infrared bands.If the absorbance of an infrared band is lower than 1.0,anomalous absorption can be suppressed thoroughly.In addition,absorption anomalies can be substantially reduced by reducing the spectral resolution of the spectrum.The reasons for anomalous absorption were discussed and how to prevent the appearance of anomalous absorption by selecting appropriate background samples were suggested.