Resonance Raman scattering and optical absorption studies of MnO4- in KClO4 at high pressure.

Abstract

We have measured the pressure dependence of both the optical absorption and the resonance Raman (RR) excitation profiles of the breathing mode, ${\ensuremath{\nu}}_{1}$, and its first two overtones for the substitutional impurity ion ${\mathrm{MnO}}_{4}^{\mathrm{\ensuremath{-}}}$, in crystalline ${\mathrm{KClO}}_{4}$. We have used the powerful transform technique of the time-correlator theory of RR scattering to analyze our RR data by calculating the profile line shapes directly from the measured optical absorption. This work constitutes the first successful application of the transform technique to the domain of high-pressure physics. The optical absorption displays a blue shift with increasing pressure, and both the ground- and excited-electronic-state vibrational frequencies increase with pressure. We calculate the renormalized Stokes loss parameter of ${\ensuremath{\nu}}_{1}$ directly from ratios of the scaling factors used in fitting our calculated profile line shapes to the data. This ``direct'' transform method presumes the broadening mechanisms to be homogeneous, and it gives a decrease in the renormalized Stokes loss parameter of less than 10% between one atmosphere and 10.6 GPa. We have also used a previously developed extension of the time-correlator theory to incorporate inhomogeneous broadening in the transform calculations. These calculations show that the effect of inhomogeneous broadening is not significant on the RR profile line shapes, but indicate that the decrease in the renormalized Stokes loss parameter with pressure could be as large as 15%.