Car-Parrinello molecular dynamics study of DCl hydrate crystals.

Three DCl hydrates have been studied using Car-Parrinello (CP) molecular dynamics. The structural results at low temperatures (T<350 K) agree with experiment and previously published CP results. The monohydrate has been shown to be built from D3O+ and Cl- ions. The dihydrate is built exclusively from D5O2+ and Cl- ions. The trihydrate consists of D2O, D5O2+, and Cl- ions. Thus, the DCl hydrates are excellent systems for studying ideal D3O+ and D5O2+ ions. The data from these ideal structures can be compared to high-concentration acid-liquid simulations. [ClD...Cl]- ions were detected at amorphous and fluid conditions after melting the di- and trihydrate crystals. The experimentally observed spectral continuum can be explained by combining the Eigen and Zundel spectra, and interpolating between the shared deuterium frequencies of the latter and the stretching band of the former.