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 α of the phonon state. For α=0 the lineshape converts into the standard Pekarian form for T=0.