LACRIDO · Laser Activated Chemistry of Reactive Intermediates: Direct Observation in the jet

The goal of LACRIDO is to lock reactive intermediates of a fast reaction by freezing them through Joules-Thompson expansion in the molecular jet, then precisely determine their three-dimensional (3D) structures by chirped-pulse microwave spectroscopy to capture all species marking the reaction mechanism.LACRIDO comprises two stages. The first stage focuses on the detection of van der Waals complexes of the educts through their 3D structures encoded in the microwave spectra. New results of the lower-risk first stage will pave the way to the higher risk-high gain second stage where reactive intermediates are formed by laser activation; adiabatically frozen and locked in the collision-free zone of the molecular jet where the rotational temperature is close to the absolute zero-point; then captured exploiting the strength of microwave spectroscopy in its specificity of conformation-sensitive detection unrivalled by any other type of spectroscopy and chemical methods.The first reaction chosen as key target is Diels-Alder, one of the most classic and important reactions in chemistry. Backed up by the Hueckel theory, Diels-Alder is theoretically described to be a single-step reaction, but details on the reaction course through the van der Waals complex of the educts have never been demonstrated experimentally and will be explored by LACRIDO, giving the final answer for an old, traditional question. The second experimental stage targets the atmospherically important reaction of isoprene with hydroxyl (OH) radical. Its reaction mechanism is extremely diverse with many steps and possible pathways to different stable products. Though lacking experimental evidence, previous studies proposed that the reaction passes through two radical intermediates, each in a cis and a trans configuration. Capturing these short-lived intermediates and determining their 3D structures would give the decisive proof, directly extracted from experiments, on the reaction paths actually taken.