简介:Here we report a detailed study on spectroscopy, structure and dynamics of water molecules at
air/water interface, investigated with Sum Frequency Generation Vibrational Spectroscopy (SFGVS).
Quantitative polarization 简介:Here we report a detailed study on spectroscopy, structure and dynamics of water molecules at
air/water interface, investigated with Sum Frequency Generation Vibrational Spectroscopy (SFGVS).
Quantitative polarization and experimental configuration analysis of the SFG data in different
polarizations with four sets of experimental configurations can shed new lights on our present
understanding of the air/water interface. Firstly, we concluded that the motion of the interfacial
water molecules can only be in a limited angular range, instead rapidly varying over a broad angular
range in the vibrational relaxation time suggested previously. Secondly, because different vibrational
modes of different molecular species at the interface has different symmetry properties, polarization
and symmetry analysis of the SFG-VS spectral features can help assignment of the SFG-VS spectra
peaks to different interfacial species. These analysis concluded that the narrow 3693cm−1 and broad
3550cm−1 peaks belong to C∞v symmetry, while the broad 3250cm−1 and 3450cm−1 peaks belong
to the symmetric stretching modes with C2v symmetry. Thus, the 3693cm−1 peak is assigned to
the free OH, the 3550cm−1 peak is assigned to the single hydrogen bonded OH stretching mode,
and the 3250cm−1 and 3450cm−1 peaks are assigned to interfacial water molecules as two hydrogen
donors for hydrogen bonding (with C2v symmetry), respectively. Thirdly, analysis of the SFG-VS
spectra concluded that the singly hydrogen bonded water molecules at the air/water interface have
their dipole vector direct almost parallel to the interface, and is with a very narrow orientational
distribution. The doubly hydrogen bond donor water molecules have their dipole vector point away
from the liquid phase.详细>