After the Fukushima accident, it became essential to have a way to monitor in real time the evolution of a nuclear reactor during a severe accident, in order to react efficiently and minimize the industrial, ecological and health consequences of the accident. Among gaseous fission products, the tetroxide of ruthenium RuO$_4$ is of prime importance since it has a significant radiological impact. Ruthenium is a low volatile fission product but in case of the rupture of the lower head by the molten corium, the air entering into the vessel oxidizes Ru into gaseous RuO$_4$, which is not trapped by the Filtered Containment Venting Systems. To monitor the presence of RuO$_4$ allows making a diagnosis of the core degradation and quantifying the release into the atmosphere.To monitoring the presence of RuO$_4$, FTIR measurement was selected. To study the feasibility of the monitoring, high-resolution IR measurements were realized at the French synchrotron facility SOLEIL on the infrared beam line AILES. Thereafter theoretical calculations were done to simulate the FTIR spectrum to describe the specific IR fingerprint of the molecule for each isotope and based on its partial pressure in the air.