Infrared-induced chemical reactions modelling

• Grant number: 23/13220-0
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor
• Start date: March 01, 2024
• End date: February 28, 2025
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Physical-Chemistry
• Principal Investigator: Ataualpa Albert Carmo Braga
• Grantee: Leonardo José Duarte
• Supervisor: Rui Fausto Martins Ribeiro da Silva Lourenço
• Host Institution: Instituto de Química (IQ). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Universidade de Coimbra (UC), Portugal
• Associated to the scholarship: 22/09269-1 - Infrared induced chemical changes: Reaction mechanisms, electronic, energy and topological factors, BP.PD

Abstract

Recent studies in spectroscopy have demonstrated that infrared radiation can induce precise and selective conformational changes and/or the breaking of chemical bonds. When infrared radiation is absorbed by the molecule, vibrational excitation occurs raising the energy of the system, consequently increasing the probability of the system tunneling through the potential barrier. Additionally, there is also the effect of Intramolecular Vibrational energy Redistribution (IVR) from the excited normal coordinate to a normal coordinate compatible with the reaction. Despite the first observation of this effect being made in 1963, instrumental limitations prevented the refinement of the technique, difficulties that have only been overcome in the last decade, making this a bleeding edge research topic. The present project is an extension of the initial postdoctoral project aimed at developing a theoretical methodology for studying the antenna effect. So far, the model is capable of reproducing infrared spectra and can simulate the dynamics of radiation-induced excitations and emissions. The model is scalable, allowing its application in systems with many atoms, limited only by the time required to obtain a good description of the potential surface. Another feature of the model is the need for experimental observations that provide clues about the normal coordinates to be investigated, justifying collaboration with the overseas group. As a test of the model, we used the cis ’ trans isomerization of nitrous acid, HONO, which occurs upon excitation of the OH stretching. The model was able to correctly predict the frequencies and intensities of fundamental bands and overtones, the timescale required for vibrational energy redistribution, and the preference for cis ’ trans isomerization over trans ’ cis isomerization, which is consistent with the literature. (AU)