ИСТИНА

The formation of femtochemistry as a new branch of chemical physics is inextricably linked to the development of a unique tool – ultrafast lasers (10–100 fs). This technology provides unprecedented temporal resolution, enabling the detection of the smallest changes in internuclear distances in molecules (~0.1 Å) and the direct observation of transition-state dynamics in chemical reactions in real time. Moreover, femtosecond laser pulses have opened qualitatively new possibilities for controlling atomic and molecular systems. The development of mid-IR laser sources, resonant with fundamental vibrational transitions in gases, allows selective excitation of target vibrational modes of molecules in the ground electronic state. This approach holds potential for overcoming the limitations imposed by rapid intramolecular vibrational energy redistribution (IVR). Suppressing IVR is crucial for controlling chemical transformations with selectivity toward specific chemical bonds or groups of bonds. This field of research enables addressing fundamental questions of chemical dynamics at a new level, verifying and refining existing theoretical models, identifying the boundaries of their applicability, and discovering novel pathways for reactivity control. The excitation regime of polyatomic gases with ultrashort mid-IR laser pulses (4.5 μm, 200 fs) is studied using the pump-probe technique. A key feature of femtosecond excitation is the ability to control the competition between multiphoton excitation and dissociation. Such control is promising both for uncovering the fundamental nature of ultrafast chemical reactions and, from an applied perspective, for laser-induced semiconductor etching in a buffered gas medium (e.g., "black silicon"). The equipment used in this work was purchased with the support of the Program for the Development of Moscow State University and the National Project “Science and Universities.”