On the cluster composition of supercritical water combining molecular modeling and vibrational spectroscopic data.

International audienceThe present study is aimed at a detailed anal. of supercrit. H2O structure based on the combination of exptl. vibrational spectra as well as mol. modeling calcns. of isolated H2O clusters. The authors propose an equil. cluster compn. model where supercrit. H2O is considered as an ideal mixt. of small H2O clusters (n = 1-3) at the chem. equil. and the vibrational spectra are expected to result from the superposition of the spectra of the individual clusters, Thus, it was possible to ext. from the decompn. of the midinfrared spectra the evolution of the partition of clusters in supercrit. H2O as a function of d. The cluster compn. predicted by this model is quant. consistent with the near IR and Raman spectra of supercrit. H2O analyzed using the same procedure. The authors emphasize that such methodol. could be applied to det. the portion of cluster in H2O in a wider thermodn. range as well as in more complex aq. supercrit. solns. (c) 2010 American Institute of Physics. [on SciFinder(R)

Calculation of IR frequencies and intensities in electrical and mechanical anharmonicity approximations: Application to small water clusters.

International audienceThe authors present a method for automatic computation of IR intensities using parallel variational multiple window CI wave functions (P_VMWC2 algorithm). Inclusion of both mech. and elec. anharmonic effects permits fundamental vibrational frequencies, including combinations and overtones, to be assigned. The authors use these developments to interpret the near-IR (NIR) and mid-IR (MIR) spectra of individual H2O clusters (H2O)n (n = 1-4). Cyclic and linear systems were studied to provide equiv. ref. theor. data to study the structure of H2O as a function of d. using NIR and MIR exptl. spectra. Various d. functional theory methods for generating the potential energy surface were compared to ref. results obtained at the CCSD(T) level. For cyclic clusters, the IR intensities and frequencies obtained using B1LYP/cc-pVTZ are in very good agreement with the available exptl. values and of the same orders of magnitude as the ref. theor. values. These data are completed by the vibrational study of linear systems. (c) 2010 American Institute of Physics. [on SciFinder(R)