Inelastic N_2+H_2 collisions and quantum-classical rate coefficients: large datasets and machine learning predictions

Abstract

Rate coefficients for vibrational energy transfer are calculated for collisions between molecular nitrogen and hydrogen in a wide range of temperature and of initial vibrational states (vle 40 for N_2 and wle 10 for H_2). These data are needed for the modelling of discharges in N_2/H_2 plasma or of atmospheric and interstellar medium chemistry in different temperature ranges. The calculations were performed by a mixed quantum-classical method, to recover quantum effects associated with the vibrational motion, on a refined potential energy surface. The obtained rates present striking discrepancies with those evaluated by first-order perturbation theories, like the SSH (Schwartz, Slavsky, Herzfeld) theory, which are often adopted in kinetic modelling. In addition, we present a detailed, though preliminary, analysis on the performance of different Machine Learning models based on the Gaussian Process or Neural Network techniques to produce complete datasets of inelastic scattering rate coefficients. Eventually, by using the selected models, we give the complete dataset (i.e., covering the whole vibrational ladder) of rate coefficients for the textrm{N}_2(v)+textrm{H}_2(0) longrightarrow textrm{N}_2(v-Delta v)+textrm{H}_2(0), Delta v=1,2,3 processes.Graphical abstract