红外吸收峰的位置波动:归因于单一谱带的频移还是重叠谱带相对强度的变化?

Positional Fluctuation of IR Absorption Peaks: Frequency Shift of a Single Band or Relative Intensity Changes of Overlapped Bands?

红外吸收峰的位置波动可能由单一谱带的实际频移或是邻近重叠谱带相对强度的变化而产生。本文通过主成分分析法(PCA)有力地证明了光谱位置波动的根源往往归因于后一种机理。PCA能灵敏有效地区分单一谱带的实际频移与由重叠谱带相对强度变化所产生的最大峰移。对于由分子相互作用强度变化所诱导,并在振动光谱领域较为常见的所谓"带移"的概念,往往由于其隐含了谱带的固有频移而有些概念误导。在许多红外光谱中,峰极大值表面的位移,一般产生于两条重叠谱带相对贡献的变化,而不是分子相互作用强度变化所诱导的单一谱带的缓慢频移。这个观点可以帮助我们解释振动光谱所探测到的分子相互作用。

Positional fluctuation of infrared peaks may be caused by the actual frequency shift of a single band or alternatively by the relative intensity changes of closely overlapped bands. This article demonstrates that the origin of positional fluctuation of spectral features may often be caused by the latter mechanism, which can be determined effectively using principal component analysis （PCA）. PCA is a sensitive tool to detect the difference between the true frequency shift of a single band and apparent peak maximum shift caused by relative intensity changes of overlapped adjacent bands. The notion of so-called ＂band shift＂ induced by the change in the strength of molecular interaction, which is well-entrenched in the field of vibrational spectroscopy, is somewhat misleading since it implicitly suggests the intrinsic shift of the band frequency. In many IR spectra, the apparent positional shifts of peak maxima seem to occur due to relative contribution changes of two overlapped bands, instead of the gradual frequency shift of a single band induced by the change in the strength of molecular interactions. The insight should help the interpretation of molecular interactions probed by vibrational spectroscopy.