Despite decades of intense research, the production of large amounts of nitrogen atoms remains a major roadblock for many industrial applications such as the enhancement of nitridation processes, the synthesis of novel nanomaterials and large band gap nitrides for high power electronics, or biomedical treatment. It is also important to understand the mechanisms of N production/removal in plasma-assisted combustion and pollutant abatement. This collaborative project seeks to elucidate the pathways of production of atomic species, particularly nitrogen, using nanosecond and microwave plasma discharges with high energy density. The project will focus on the kinetic mechanisms involving electronically excited states of N2. In nitrogen plasmas, many electronic excited states with energies greater than 11.5 eV are produced by electron impact reactions under the action of high electric fields. These excited states can spontaneously predissociate, forming nitrogen atoms in the ground state N(4S) and in the first two excited metastable states, N(2P) and N(2D). This route is the dominant pathway for nitrogen dissociation at low pressures where collisions between neutral species are infrequent. At higher pressure, however, these excited states can also dissociate by collisions with ground state nitrogen molecules. Some authors predict that collisional dissociation prevails over predissociation at pressures above a few atmospheres. Other processes that become important at high pressure (typically above a fraction of an atmosphere) include pooling reactions by which two electronically excited molecules of nitrogen collide and dissociate one of them. Despite this apparent beneficial effect of operating at high pressures, it should be noted that two and three-body recombination of nitrogen atoms also increases with the pressure, thus potentially reducing the overall nitrogen atom production. Because the rates of collisional excitation by electron impact increases exponentially with the reduced electric field E/N, where E is the electric field and N the total gas number density, it is also expected that the density of electronically excited states increases with E/N. Thus higher reduced fields result in higher dissociation of nitrogen atoms and a lower energy cost per atom produced. Typical values reported in the literature indicate that the energy cost is about 340 eV/atom at E/N = 140 Td (1 Td = 10-17 V-cm2), and it decreases to values as low as 40 eV/atom above 300 Td. Few experimental results have been reported in the literature to confirm these trends over a wide range of reduced electric fields and pressures. Thus, the objective of this project is to improve our understanding of these processes. To this end, we will perform experiments with several plasma discharges capable of operating from the non-collisional regime (1-10 Pa) to the highly collisional regime at 10 atm, with reduced electric fields from 100 to 400 Td. Advanced diagnostic techniques, namely femto-, pico-, and nano-second TALIF and quantitative OES will be developed to quantify the density of ground and excited species. In parallel, kinetic and discharge models will be developed to guide and analyze the measurements. The expected outcomes include a detailed understanding of nitrogen production kinetics, and a comparison of the various types of discharges over the wide range of pressures and reduced electric fields investigated that will serve as a reference to guide the needs of the applications envisioned. The consortium assembles a complementary team of experts in plasma discharge characterization, plasma modeling, and advanced optical diagnostics. We will also benefit from international collaborations with leading experts in chemical mechanisms, in particular the Chemistry group of Prof. Capitelli (University of Bari), and N. Popov (Moscow State University) who participates in the LIA of one of the project partners.