title: Gas-phase preparation of carbonic acid and its monomethyl ester.
abstract: Carbonic acid (H2CO3), an essential molecule of life (e.g., as bicarbonate buffer), has been well characterized in solution and in the solid state, but for a long time, it has eluded its spectral characterization in the gas phase owing to a lack of convenient preparation methods; microwave spectra were recorded only recently. Here we present a novel and general method for the preparation of H2CO3 and its monomethyl ester (CH3OCO2H) through the gas-phase pyrolysis of di-tert-butyl and tert-butyl methyl carbonate, respectively. H2CO3 and CH3OCO2H were trapped in noble-gas matrices at 8 K, and their infrared spectra match those computed at high levels of theory [focal point analysis beyond CCSD(T)/cc-pVQZ] very well. Whereas the spectra also perfectly agree with those of the vapor phase above the β-polymorph of H2CO3, this is not true for the previously reported α-polymorph. Instead, the vapor phase above α-H2CO3 corresponds to CH3OCO2H, which sheds new light on the research that has been conducted on molecular H2CO3 over the last decades.
authors.affiliation: Institute of Organic Chemistry, Justus-Liebig-University, Heinrich-Buff-Ring 58, 35392 Giessen (Germany).
authors.forename: Hans Peter
authors.initials: HP
authors.lastname: Reisenauer
authors.forename: J Philipp
authors.initials: JP
authors.lastname: Wagner
authors.forename: Peter R
authors.initials: PR
authors.lastname: Schreiner
mesh_terms: D002255:Carbonic Acid / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
chemical_list: D005740:Gases; D002255:Carbonic Acid
keywords: IR spectroscopy; ab initio calculations; ester pyrolysis; matrix isolation