ULTRAFAST COHERENT VIBRONIC DYNAMICS IN COLOR-CENTERS

Recent femtosecond pump-probe experiments on KBr F-centers are interpr eted using a density matrix scheme for the breathing modes and a calcu lation of the time evolution of a wave packet for the local vibrations of lower symmetry. The elongations of all modes are derived from stat ionary absorption measurements, while the frequencies and dephasing ti mes of the breathing modes are taken from the femtosecond pump-probe r esults. With a density matrix calculation for the breathing modes we a chieve quantitative agreement with the oscillation pattern observed in the femtosecond experiments without free parameters. The time integra tion of an excited wave packet in the product space of the d-symmetric local vibrations and the excited p states gives insight into the obse rved ultrafast reorientation of the excited p state. (C) 1998 Elsevier Science B.V. All rights reserved.