The early quantum dynamics following the B(3Pi{0u^+}) <- X photoexcitation of I2 in large
rare gas clusters is
studied and the resonance Raman spectrum of these systems is calculated
by a novel time-dependent quantum mechanical simulation approach.
The method used is the
Classically-Based Separable Potential (CSP) approximation, in which classical
Molecular Dynamics simulations are used in a first step to determine
an effective time-dependent separable
potential for each mode, then followed by quantum wavepacket calculations
using these potentials.
In the simulations for I2(Ar)n and I2(Xe)n, with n=17,47, all the
modes are treated quantum mechanically.
The Raman overtone intensities are computed from the multidimensional
time-dependent wavepacket for each system, and the results are compared with
experimental data on I2 in Ar matrices and in liquid Xe. The main findings
include: i) Due to wavepacket dephasing effects the Raman spectra are determined
well before the iodine atoms hit the rare gas 'wall' at about 80 fs after
photoexcitation. ii) No recurrencies are found in the correlation functions
for I2(Ar)n. A very weak recurrence event is found for I2(Xe)n.
iii) The simulations for I2(Ar)17 (first solvation layer) and for
I2(Ar)47 (second solvation shell) show differences corresponding to
moderate cluster size effects on the Raman spectra. iv) It is estimated
that coupling to the B"(1Pi{1u}) state or to the a(1g) state have a small
effect on the Raman intensities. v) For I2(Ar)47, the results
are in very good quantitative agreement with I2/Ar matrix experiments. The
I2(Xe)n results are in qualitative agreement with experiments on I2
in liquid Xe. The reported calculations represent a first modeling of resonance
Raman spectra by quantum dynamical simulations that include all degrees of
freedom in large systems, and they demonstrate the power of the CSP method in this respect.