Formation of H 3 O + and OH by CO 2 and N 2 O trace gases in the atmospheric environment.

The impact of cosmic rays' energetic subatomic particles on climate and global warming is still controversial and under debate. Cosmic rays produce ions that can trigger fast reactions affecting chemical networks in the troposphere and stratosphere especially when a large amount of relevant trace gases such as carbon dioxide, methane, sulfur dioxide and water are injected by volcanic eruptions. This work focuses on synchrotron experiments and an ab initio theoretical study of the ion chemistry of carbon dioxide and nitrous oxide radical cations reacting with water. These molecules catalyze a fast exothermic formation of hydronium ions H 3 O + and the hydroxyl radical OH, the main oxidant in the atmosphere. Moreover, theoretical calculations demonstrate that at the end of the catalytic cycle, CO 2 and N 2 O are produced vibrationally excited and subsequently they quench in the microsecond time scale by collision with the surrounding atmospheric molecules at the pressure and temperature of the upper-troposphere/stratosphere. The chemistry involved in these reactions has a strong impact on the oxidant capacity of the atmosphere, on the sulfate aerosol production, on the cloud formation and eventually on the chemical networks controlling climate and global warming models.