Local Structures of Methanol–Water Binary Solutions Studied by Soft X-ray Absorption Spectroscopy (original) (raw)

Liquid methanol shows one-and two-dimensional (1D/2D) hydrogen bond (HB) networks, and liquid water shows three-dimensional (3D) HB networks. We have clearly found three different local structures around the methyl g r o u p o f m e t h a n o l − w a t e r b i n a r y s o l u t i o n s (CH 3 OH) X (H 2 O) 1−X at different concentrations in C K-edge soft X-ray absorption spectroscopy (XAS). With the help of molecular dynamics simulations, we have discussed the concentration dependence of the hydrophobic interaction at the methyl group in the C K-edge XAS spectra. In the methanol-rich region I (1.0 > X > 0.7), a small amount of water molecules exists separately around dominant 1D/2D HB networks of methanol clusters. In the region II (0.7 > X > 0.3), the hydrophobic interaction of the methyl group is dominant due to the increase of mixed methanol−water 3D network structures. In the waterrich region III (0.3 > X > 0.05), methanol molecules are separately embedded in dominant 3D HB networks of water. On the other hand, the pre-edge feature in the O K-edge XAS shows almost linear concentration dependence. It means the HB interaction between methanol and water is almost the same as that of water−water and of methanol−methanol.