Coherent-phonon vibronic sideband

We present the theory of vibronic sideband spectra due to coherent phonon modes using the conventional model of linear electron-phonon coupling and displaced equilibrium positions of the oscillators in the exited and final electronic states. Unlike in the conventional theory the initial state of the oscillator is taken as a coherent phonon state and not as a thermalized one. Under these conditions we got an exact analytical solution for the lineshape of the vibronic sideband. The sideband is determined by two parameters, the Huang-Rhys parameter S and the coherence parameter g. of the phonon state. For alpha = 0 the lineshape converts into the standard Pekarian form for T = 0. (c) 2006 Elsevier B.V. All rights reserved.