In the case of straddling molecules with one hydrogen in water, when compared to bonds below the surface, "the hydrogen bond is surprisingly only slightly weaker," according to Benderskii.
Likewise, the bond for the hydrogen atom sticking out of the water is similar in strength to bonds in the gas phase.
The researchers concluded that the change between air and water happens in the space of a single water molecule.
"You recover the bulk phase of water extremely quickly," Benderskii said.
While the transition happens in the uppermost layer of water molecules, the molecules involved change constantly. Even when they rise to the top layer, molecules for the most part are wholly submerged, spending only a quarter of their time straddling air and water.
The study raises the question of how exactly to define the air-water boundary.
If the straddling molecules constitute the boundary, it would be analogous to a wood fence where three of every four boards are missing except that since water molecules always are moving between submerged and straddling positions, the location of the fourth board would change millions of times per second.
If the boundary were the entire top layer of water molecules, the analogy would be a fence where one in four boards is sticking out at any one time.
|Contact: Carl Marziali|
University of Southern California