Theory of coherent four-photon spectroscopy of electron resonances in molecular systems

A quantum theory of coherent four-photon spectroscopy of electron resonances in molecular systems is developed. A model allowing for real properties of the dispersion of perturbations modulating electron transitions in complex molecules is considered. New relationships are established between the characteristics of spectra of one-photon absorption and the law governing the dispersion of a signal obtained in steady-state four-photon spectroscopy, conditions for excitation of this signal, its dispersion, etc. It is shown that the theory agrees with the available experimental data.