Configuration Coordinate Model for theFCenter in KBr

摘要

Experimental absorption curves for theFcenter in KBr, after correction forKhyphen;band absorption, have been analyzed in terms of the semiclassical configuration coordinate model with linear and quadratic coupling. This model fits the absorption data well at both the lowhyphen;temperature and highhyphen;temperature limits. The best fit to the data is found by varying five parameters: These are the force constants in the ground and excited states, the photon energy corresponding to the maximum in the absorption band (Em), the relative displacement of the minima of the adiabatic potentials for the ground and excited states, and the effective frequency of the vibration which is coupled to the ground electronic state. Consistent values of the parameters are found at both temperature limits. An expression is derived for the shift ofEmwith temperature. It is pointed out that not only isEmnot identical with the average photon energy but that its temperature dependence actually has the opposite sign. The theory is tested by predicting the temperature shift ofEm; after suitable corrections for thermal expansion the agreement with experimental data is surprisingly satisfactory.