Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published May 20, 2010 | Supplemental Material
Journal Article Open

Proton Availability at the Air/Water Interface


The acidity of the water surface sensed by a colliding gas is determined in experiments in which the protonation of gaseous trimethylamine (TMA) on aqueous microjets is monitored by online electrospray mass spectrometry as a function of the pH of the bulk liquid (pH_(BLK)). TMAH^+ signal intensities describe a titration curve whose equivalence point at pH_(BLK) 3.8 is dramatically smaller than the acidity constant of trimethylammonium in bulk solution, pK_A(TMAH^+) = 9.8. Notably, the degree of TMA protonation above pH_(BLK) 4 is enhanced hundred-fold by submillimolar LiCl or NaCl and weakly inhibited at larger concentrations. Protonation enhancements are associated with the onset of significant direct kinetic solvent hydrogen isotope effects. Since TMA(g) can be protonated by H_2O itself only upon extensive solvent participation, we infer that H3O^+ emerges at the surface of neat water below pH_(BLK) 4.

Additional Information

© 2010 American Chemical Society. Received Date: March 12, 2010. Accepted Date: April 26, 2010. Published on Web Date: May 03, 2010. S.E. appreciates the Japan Society for the Promotion of Sciences Postdoctoral Fellowships for Research Abroad. We thank Nathan Dalleska for expert help with some experiments. This work was supported by National Science Foundation Grant ATM-0714329.

Attached Files

Supplemental Material - jz100322w_si_001.pdf


Files (81.2 kB)
Name Size Download all
81.2 kB Preview Download

Additional details

August 19, 2023
October 20, 2023