From N(2) and O(2) to N(4) and O(4): pneumatic chemistry in the 21st century

A brief account is given of the theoretical and experimental endeavors that span the last decade and eventually led to the discovery of N(4) and O(4), which have been actively sought for their fundamental interest and their relevance to atmospheric sciences and the development of high energy density materials (HEDM). The discovery and characterization of N(4) and O(4) as metastable species with lifetimes exceeding 1 micros in the isolated gas state have finally been achieved utilizing neutralization-reionization mass spectrometry (NRMS), a powerful technique based on collisional redox processes. The principles of NRMS, experimental outline, main features, and limitations are succinctly examined in comparison with other current approaches to the detection of metastable, short-lived neutral species.