Theoretical ground for precursors-based molecular spectroscopy

A theory for excitation of molecular resonances by a train of precursors is developed. Right at the vacuum-medium interface, a train of incident square waves interacts with light electrons and is converted into a train of precursors, which further excite molecular dipoles. Analytic calculations indicate that these excited dipoles generate radiation, including secondary precursors propagating in the backward direction. Encoded in this radiation are proper frequencies of excited molecular dipoles allowing for spectroscopic measurements. The frequency of the train of incident square pulses can be by several orders of magnitude smaller than the proper frequencies of molecular resonances.