Identification of overlapping features in the sum frequency generation vibrational spectra of air/ethanol interface

The stretching vibrations of the –CH3 and –CH2– groups not only overlap but also interfere with each other in the Sum-Frequency Generation (SFG) vibrational spectra of the air/ethanol interface. Using deuterated ethanol samples, i.e., CH3CD2OH and CD3CH2OH, the C–H stretching vibrational modes are clearly assigned for the SFG vibrational spectra of their air/liquid interfaces according to the polarization selection rules. It is found that the CH3-ss and CH2-ss modes overlap in the ∼2875 cm−1 peak, the CH3-as and CH2-ss-Fermi modes overlap in the ∼2970 cm−1 peak, and the ∼2930 cm−1 peak belongs to the CH3-ss-Fermi mode, respectively.