  The short-range structure of an iron doped soda-lime glass was investigated
by infrared emissivity spectroscopy from room temperature up to the melt.
Quantitative information on the distribution of the Q^n tetrahedral units was
obtained by fitting the emissivity spectra using a dielectric function model
(DFM). The DFM is based on causal Gaussian bands, associated with the
stretching motions of the silicate tetrahedra. The changes in the absorption
modes are related to the activation of a dynamical disorder that continuously
increases with temperature. The obtained Q^n speciation at room temperature is
in good agreement with the magic-angle spinning nuclear magnetic resonance (MAS
NMR) study. The distribution of the tetrahedral species undergoes slight
changes with temperature, except during glass crystallization where Q^4 units
increases, with a slight augmentation of Q^2 and Q^4 units in the melt. These
results demonstrate the potentiality of infrared spectroscopy in the
quantitative analysis of the polymerization degree of glasses and melts.
