Experimental and theoretical study on Raman spectra of magnesium fluoride clusters and solids

In this study, the Raman and IR spectra of a large number of isomers of MgF2 clusters and of possible bulk polymorphs of MgF2 are calculated and compared with experimental data observed using a low-temperature atom beam deposition. The bulk polymorphs were taken from earlier work, while the cluster modifications for the neutral (MgF2)(n) (n = 1-10) clusters and charged clusters (up to the trimer anion and cation, (Mg3F7)(-) and (Mg3F5)(+), respectively) are determined in the present work by global energy landscape explorations using simulated annealing. These theoretical calculations are complemented by an experimental study on both the vapor phase and the deposited films of MgF2, which are generated in a low-temperature atom beam deposition setup for the synthesis of MgF2 bulk phases. The MgF2 vapor and film are characterized via Raman spectroscopy of the MgF2 gas phase species embedded in an Ar-matrix and of the MgF2-films deposited onto a cooled substrate, respectively. We find that, in the vapor phase, there are monomers and dimers and charged species to be present in our experimental setup. Furthermore, the results suggest that in the amorphous bulk MgF2, rutile-like domains are present and MgF2 clusters similar to those in the matrix. Finally, peaks at about 800 cm(-1), which are in the same range as the A(g) modes of clusters with dangling fluorine atoms connected to three-coordinated Mg atoms, indicate that such dangling bonds are also present in amorphous MgF2. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4765700]