METASTABLE INTERMEDIATES FROM GLASSY SOLUTIONS .3. FTIR SPECTRA OF ALPHA-CARBONIC ACID AND ITS H-2 AND C-13 ISOTOPIC FORMS, ISOLATED FROM METHANOLIC SOLUTION

Layers of glassy solutions of (KHCO3)-C-12 ((KDCO3)-C-12, (K2CO3)-C-13 ) and of excess HCl (DCl) dissolved in CH3OH (CH3OD) and in 70 wt.% gl ycerol-water have been deposited sequentially at 78 K in the form of d roplets, and their reaction in the temperature range 78-300 K studied by FTIR spectroscopy (from 4000 to 400 cm(-1)). At ca. 20 K above the glass-transition temperature(T-g) of the solvent, a decrease in viscos ity initiated coalescence of the droplets. At ca. 40 K above T-g, prot onation of the hydrogen carbonate (carbonate) and formation of H2CO3 o ccurred in the liquid state. After pumping off the solvent, residual i ce and excess HCl, amorphous (H2CO3)-C-12 ((D2CO3)-C-12, (H2CO3)-C-13) was isolated, crystallizing at ca. 190-200 K to alpha-carbonic acid. Assignments for the spectral features of alpha-H2CO3 and its isotopic forms are given. Base pressure, water content and heating rate lead to varying degrees of disorder in the crystalline phase. The cryogenic m ethod for formation of metastable short-lived intermediates from react ion of non-volatile reactants is discussed. The intermediates can be s tudied in solution or as amorphous or crystalline solids.