Nitrogen Oxide Production in Laser‐Induced Breakdown Simulating Impacts on the Hadean Atmosphere

The high‐energy‐density synthesis of NxOyspecies is simulated in gas mixtures representing an O2‐free early‐Earth atmosphere by terawatt‐kilojoule‐class laser‐induced dielectric breakdown (LIDB). These experiments differ from previous LIDB experiments due to the 100 times greater energy delivered per pulse and sensitive analysis of products by high‐resolution infrared spectroscopy. The measured yields of NO, N2O, and NO2are 0.08–8 × 1015, 5 × 1012, and 0.03–7 × 1014molec J −1. The high N2O yield is above the upper‐limit constraint of previous tabletop LIDB experiments and the expected yield of a thermochemical freeze‐out at any temperature between 2000 and 5000 K, while the NO and NO2yields are in broad agreement with freeze‐out models. Using a one dimensional chemical model of the Hadean atmosphere and a simple model of late bombardment, we compute the source flux of N2O assuming the same high production yield as measured experimentally and find the steady‐state partial pressure of N2O is insufficient to warm the climate. The climate of the Earth 4.5 to 4 billion years ago is not well known but geological evidence suggests the presence of liquid water, which is at odds with the possibility of a very‐cold early Earth. Extra greenhouse warming by atmospheric gases is thought necessary to keep the surface temperature high enough for liquid water. Nitrous oxide is a possible greenhouse gas and its high‐temperature formation in an atmosphere undergoing intense meteor bombardment may provide additional means of warming the early Earth. In this paper, we mimic the impact formation of nitrogen oxide molecules in the laboratory using a high‐energy laser‐induced plasma. The laser generates pulses 100 times more energetic than in previous studies and the new molecules are measured by infrared spectroscopy. We then compute the stable amount of nitrous oxide that might have existed 4.5 billion years ago and find this is still too small to contribute to greenhouse warming. The effect of large amounts of impact‐formed nitrogen oxides may still lead to significant short‐term consequences of a large impact, or become chemical inputs to the first stages of biochemistry, or be relevant for observational models exoplanet atmospheres in young star systems encountering heavy bombardment. A terawatt‐class laser simulation of NxOyformation by impacts finds a large yield of N2OOne‐dimensional atmospheric model shows that impact‐production of N2O is still insufficient to significantly warm the Hadean Earth A terawatt‐class laser simulation of NxOyformation by impacts finds a large yield of N2O One‐dimensional atmospheric model shows that impact‐production of N2O is still insufficient to significantly warm the Hadean Earth