Bereiche | Tage | Auswahl | Suche | Downloads | Hilfe

MO: Fachverband Molekülphysik

MO 8: Femtosekundenspektroskopie 2

MO 8.4: Vortrag

Dienstag, 3. März 2009, 14:45–15:00, VMP 6 HS-F

Observation of carbonic acid in aqueous solution upon ultrafast protonation of bicarbonate — •Katrin Adamczyk¹, Mirabelle Prémont-Schwarz¹, Dina Pines², Ehud Pines², and Erik T. J. Nibbering¹ — ¹Max Born Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max Born Strasse 2A, D-12489 Berlin, Germany — ²Department of Chemistry, Ben-Gurion University of the Negev, P.O.B. 653, Beer-Sheva 84125, Israel

It is generally assumed that carbonic acid, H2CO3, is not stable, but instead decomposes into CO2 and H2O. However, the Schwarz and Mayer groups have recently shown that H2CO3 can be detected as isolated molecules in the gas phase, or in ice matrices. In contrast, H2CO3 in aqueous solution has not been reported on, because water is understood to catalyse its decomposition. On the other hand, H2CO3 is often postulated as intermediate between CO2 and HCO3*, by way of an acid-base equilibrium, and its characterization would be of substantial support in understanding fundamental acid-base chemistry of carbonates in aqueous solution as well as in biophysical situations. Here we present for the first time femtosecond infrared spectroscopic results showing unequivocal support for the existence of carbonic acid in aqueous conditions, formed after ultrafast protonation of HCO3* using a photoacid as a means of optically-triggered titration. By analysing the time-dependent signal magnitude of vibrational marker modes using the Szabo-Collins-Kimball approach to describe bimolecular reaction dynamics subject to the Debye-von Smoluchowski diffusional equation, an on-contact proton transfer reaction rate is derived.