A review is given of the physical phenomena observed when polyatomic molecules interact with intense infrared radiation pulses. A brief historical account is given of earlier investigations and the main processes are classified. Then, the following topics are considered: 1) multiphoton infrared absorption and transition of molecules through lower vibrational levels; 2) dynamics of molecular excitation in a vibrational quasicontinuum and distribution of the vibrational energy between the modes and levels; 3) dissociation of highly excited molecules. The main experimental and theoretical results, and possible future trends are discussed. The review concludes with a brief list and illustrations of typical applications of the phenomena described in molecular spectroscopy, chemical physics, nuclear chemistry, and chemical synthesis.

@article{Letokhov:1981,
	author = {V. S. Letokhov and A. A. Makarov},
	title = {Polyatomic molecules in a strong infrared field},
	publisher = {Physics-Uspekhi},
	year = {1981},
	journal = {Phys. Usp.},
	volume = {24},
	number = {5},
	pages = {366-393},
	url = {https://ufn.ru/en/articles/1981/5/b/},
	doi = {10.1070/PU1981v024n05ABEH004833}
}