[Application of wavenumber-linear scaling to the calculated Raman frequencies of polyenes and carotenoids].

Raman spectra of two typical carotenoids (beta-carotene and lutein) and some short (n = 2-5) polyenes were calculated using density functional theory. The wavenumber-linear scaling (WLS) and other frequency scaling methods were used to calibrate the calculated frequencies. It was found that the most commonly used uniform scaling (UFS) method can only calibrate several individual frequencies perfectly, and the systematic result of this method is not very good. The fitting parameters obtained by the WLS method are upsilon(obs)/upsilon(calc)) = 0.999 9-0.000 027 4upsilon(calc) and upsilon(obs)/upsilon(calc)= 0.993 8-0.000 024 8upsilon(calc) for short polyenes and carotenoids, respectively. The calibration results of the WLS method are much better than the UFS method. This result suggests that the WLS method can be used for the frequency scaling of the molecules as large as carotenoids. The similar fitting parameters for short polyenes and carotenoids indicate that the fitting parameters obtained by WLS for short polyenes can be used for calibrating the calculated vibrational frequencies of carotenoids. This presents a new frequency scaling method for vibrational spectroscopic analysis of carotenoids.