PNNL

Abstract

Tremendous progresses have been made in quantitative understanding and interpretation of the hydrogen bonding and ordering structure at the air/water interface since the first sum-frequency generation vibrational spectroscopy (SFG-VS) measurement on the neat air/water interface by Q. Du et al. in 1993 (PRL, 70, 2312-2316, 1993.). However, there are still disagreements and controversies on the consistency between the different experiment measurements and the theoretical computational results. One critical problem lies in the inconsistency between the SFG-VS intensity measurements and the recently developed SFG-VS phase spectra measurements of the neat air/water interface, which has inspired various theoretical efforts trying to understand them. In this report, the reliability of the SFG-VS intensity spectra of the neat air/water interface is to be quantitatively examined, and the sources of possible inaccuracies in the SFG-VS phase spectral measurement is to be discussed based on the non-resonant SHG phase measurement results. The conclusion is that the SFG-VS intensity spectra data from different laboratories are now quantitatively converging and in agreement with each other, and the possible inaccuracies and inconsistencies in the SFG-VS phase spectra measurements need to be carefully examined against the properly corrected phase standard.