[Zurück]

H. Grothe, R. Huber, K. Liedl, J. Bernard, T. Loerting:
"Matrix isolation studies of carbonic acid - the vapour phase above the two polymorphs";
Vortrag: TURCMOS 2013, Istanbul; 15.09.2013 - 20.09.2013; in: "Book of Abstracts", (2013), S. 52.

Carbonic acid appears as trace compenent in the natural world in solution, e.g., in soda, champagne, blood and rain . Recent work, including ours, suggests carbonic acid to exist even in pure form as a
solid in ice clouds, comets, icy moons and polar regions of planets. Twenty years ago, in the lab two different polymorphs of carbonic acid, a- and ß-H2C03, were isolated in pure form as th in, crystalline
films. They were characterized by infrared and, lately, by Raman spectroscopy. Recently, we succeeded in sublimating a-H2C03 and trapping the vapor phase in a noble gas matrix, which was analyzed by
infra red spectroscopy. In the same way we have now investigated the ß-polymorph. Unlike a-H2C03, ß-H2C03 was regarded to decompose upon sublimation. Still, we have succeeded in isolation of undecomposed carbonic acid in the matrix and recondensation after removal of the matrix here. This possibility of sublimation and recondensation cycles of ß-H 2C03 adds a new aspect to the chemistry of carbonic acid in astrophysical environments, especially because there is a direct way of ß-H2C03 formation in space, but none for a-H2C03. Assignments of the FTIR spectra of the isolated molecules
unambiguously reveal two different carbonic acid monomer conformers (C2v and Cs) . By contrast to the earlier study on a-H2C03 we do not find evidence for centrosymmetric (C2h) carbonic acid dimers
here. This suggests that two monomers are entropically favored and might even be detectable in the gas phase, e.g., in the atmosphere of Mars or Venus.

Matrix Isolation, FTIR, UV/VIS, astrophysics, atmospheric chemistry