Semiclassical molecular dynamics computation of spontaneous light emissionin the condensed phase: Resonance Raman spectra

The three-time correlation function that describes resonance Raman (RR) spe ctra is computed directly using the Herman-Kluk semiclassical propagator. T he trace expression for this correlation function {C(t(1),t(2),t(3))=Tr[e(- beta(H) over cap)e(g)(-iH)(t(1)+t(2))e(e)(-iH)t(3)e(g)(+iH)(t(2)+t(3))e(e)( +i (H) over cap)t(1)]} allows forward-backward time propagation of trajecto ries over closed time-circuits, leading to efficient convergence in multidi mensional systems. A local harmonic approximation is used to derive an expr ession for the density operator in the coherent state representation (<p(1) q(1)parallel toe(-beta(H) over cap)parallel top(2) q(2)>). This allows eff icient sampling of phase space as well as simulations at arbitrary temperat ures and in arbitrary coordinates. The resulting method is first analyzed f or a one-dimensional problem, where the results are shown to be in excellen t agreement with exact quantum calculations. The method is then applied to the problem of RR scattering of iodine in the condensed phase. The RR spect rum of an I-2 molecule in a xenon fluid at 230 K is calculated and also fou nd to be in excellent agreement with experiment. (C) 2001 American Institut e of Physics.