PROBING INTRAMOLECULAR VIBRATIONAL-ENERGY RE-DISTRIBUTION BY USING A PAIR OF FEMTOSECOND-LASER PULSES - A THEORETICAL-MODEL

We propose a method of probing intramolecular vibrational energy re-di stribution (IVR) by using a pair of femtosecond laser pulses. This doe s not rely on the idea of localized wave packets and is applicable to polyatomic molecules which undergo rapid IVR. The first pulse produces a non-stationary wavefunction composed of several vibrational eigenst ates. After a time interval, comparable with the time scale of IVR, so me components of the non-stationary wavefunction are depleted by the s econd pulse. The populations in these eigenstates are detected by obse rving dispersed fluorescence. Numerical simulations based on a coupled oscillator model demonstrate that the second pulse depletes specific components selectively. The populations after the second pulse reflect how the IVR proceeds until the second pulse is introduced. (C) 1998 E lsevier Science B.V. All rights reserved.