​In situ reaction monitoring tracks concentration changes of key reactive and transient species to understand mechanism pathway, determine kinetics and detect major reaction events. ReactIR 45m is a real-time, in situ mid-infrared based system designed to study reaction progression and provide specific information about reaction initiation, conversion, intermediates and endpoint. The reactor uses a specially designed optical fiber equipped with an ATR sensor at the tip to channel the signal from the IR source to reaction media and back to the MCT detector. This equipment can be used for applications at temperatures from -80 to 180 °C and pressures up to 10 barg.