DETERMINATION OF THE DEGREE OF ANHARMONICITY BY CLASSICAL DISPERSION ANALYSIS OF INFRARED REFLECTANCE DATA

Author Institution: Department of Chemistry and Hawaii Institute of Geophysics, University of HawaiiIt has been assumed that highly accurate values of dispersion parameters can be obtained by classical dispersion (CD) analysis of reflectance data, provided that the data are free of experimental errors and surface state effects. A new CD analysis technique has been developed and carefully evaluated on various combinations of synthetically generated reflectance bands which correspond to damped harmonic oscillators. For such systems this new CD technique, using a self bracketing search approach, provide highly accurate values of resonance frequency ($v_{i}$), oscillator strength ($S_{i}$) and damping constant ($\gamma_{j}$). However, the application of the new CD technique for infrared reflectance data of LiF and MgO while yielding approximately the same values of $\nu_{j}$ and $S_{j}$ as those obtained by other CD techniques, yields different values for $\gamma_{j}$. This study demonstrates, therefore, that for strongly anharmonic systems CD analysis may provide reliable values of $\nu_{j}$ and $S_{j}$ but cannot yield highly accurate values of damping constants. This study does suggest, however, that our new CD technique may be useful in determining qualitatively the “degree of anharmonicity,” for example, in some of the internal modes of $NaClO_{3}$ and in lattice modes of LiF and MgO.This research was supported in part by the National Science Foundation Grant GP-13087