Carbonic Acid in the Gas Phase and Its Astrophysical Relevance

Abstract

In outer space, high-energy irradiation of cryogenic ice mixtures of abundant water and carbon dioxide is expected to form solid carbonic acid. Experiments and thermodynamic analyses show that crystalline carbonic acid sublimates without decomposition. Free-energy considerations based on highly accurate molecular quantum mechanics, in combination with vapor pressures resulting from experimental sublimation rates, suggest that in the gas phase, a monomer and dimer of carbonic acid are in equilibrium, comparable to that of formic acid. Gaseous carbonic acid could be present in comets, on Mars and outer solar system bodies, in interstellar icy grains, and in Earth's upper atmosphere.

Density functional study of carbonic acid clusters

“…The calculations extend our earlier work on the monomer and other fragments of polycarbonate, 9 and they appear to be the first calculations for clusters larger than the dimer. 8 In addition to the geometrical structures, we calculate vibration frequencies and the energy cost of bending and stretching the clusters.…”

“…Two crystalline forms of carbonic acid have been identified, [6][7][8] and it is natural to ask whether threedimensional structures can be derived from CA clusters. Linear chains of CA can clearly give rise to extended solids bound by van der Waals interactions, but the absence of structural information suggests that we also investigate nonlinear isomers of CA clusters, even if they are less stable than their linear counterparts.…”

“…New features in the IR spectra of the resulting films were assigned to solid H 2 CO 3 trapped in the ice matrix. Hage et al 7,8 formed solid H 2 CO 3 by the reaction of K 2 CO 3 and HCl ͑and HBr͒ at 150 K in vitreous methanol films. Crystallization to a form denoted ␣-H 2 CO 3 occurred at 190-200 K, and Fourier transform infrared spectroscopy ͑FTIR͒ measurements were performed on it.…”

IR Spectra of Protonated Carbonic Acid and Its Isomeric H3O+⋅CO2 Complex

“…The authors of this Communication wish to correct a remark in their introductory paragraph: "There have been several unsuccessful attempts to generate and characterize gas-phase H 2 CO 3 by heating solid H 2 CO 3 [3] or NH 4 HCO 3 . [12] " This statement is incorrect and misleading, and the authors apologize for their oversight.…”

Cooperative effects in two-dimensional ring-like networks of three-center hydrogen bonding interactions

“…It should be mentioned that a single molecule of a carbonic acid can exist in three different minimum-energy conformations. [48][49][50][51][52][53][54][55] The most stable conformations is the trans-trans isomer, followed by the cistrans and cis-cis forms. Previous ab initio studies on the dimer of carbonic acid, with each monomer in its most stable trans-trans conformation, show that this dimer is remarkably stable.…”