Vibrational sum frequency generation of aqueous solutions of alcohol

We measured vibrational spectra of the surface of alcohol (C_nH_2n+1, n=1 to 3) and water as a binary mixture via sum frequency generation (SFG) in the OH region at the interface between air and liquid phases. Our results conform to a statement that the proportion of water molecules with a free dangling OH bond is about 29 percent at the interface between air and water. We have also demonstrated that a LiNbO₃ crystal containing -OH can be sufficient for the SFG spectroscopy measurement in OH region regardless of its absorption dip.