Cross sections, rates, equilibrium constants and vibrational relaxation times for the N(4S) + O2(X3Σ−g) ↔ O(3P) + NO(X2Π) reaction from simulations on new, RKHS-based surfaces for the three lowest electronic states.

Accurate potential energy surfaces (PESs) have been determined for the 3A' and 3A'' states of N2O using electronic structure calculations at the multireference configuration interaction level with Davidson correction (MRCI+Q)...

A new analytical potential energy surface (PES) has been constructed for H + 2 -He using a reproducing kernel Hilbert space (RKHS) representation from an extensive number of ab initio energies computed at the multi-reference and full configuration interaction level of theory. For the MRCI PES the long-range interaction region of the PES is described by analytical functions and is connected smoothly to the shortrange interaction region, represented as a RKHS. All ro-vibrational states for the ground vibrational and electronic state of H + 2 -He are calculated using two different methods to determine quantum bound states. Comparing transition frequencies for the near-dissociation states for ortho-and para H + 2 -He allows assignment of the 15.2 GHz line to a J = 2 e/f parity doublet of ortho-H + 2 -He whereas the experimentally determined 21.8 GHz line is only consistent with a (J = 0) → (J = 1) e/e transition in para-H + 2 -He. a) m.meuwly@unibas.ch

A machine-learned model for predicting product state distributions from specific initial states (state-to-distribution or STD) for reactive atom–diatom collisions is presented and quantitatively tested for the N(4S) + O2(X3Σg−) → NO(X2Π) + O(3P) reaction. The reference dataset for training the neural network consists of final state distributions determined from quasi-classical trajectory (QCT) simulations for ∼2000 initial conditions. Overall, the prediction accuracy as quantified by the root-mean-squared difference (∼0.003) and the R2 (∼0.99) between the reference QCT and predictions of the STD model is high for the test set, for off-grid state-specific initial conditions, and for initial conditions drawn from reactant state distributions characterized by translational, rotational, and vibrational temperatures. Compared with a more coarse grained distribution-to-distribution (DTD) model evaluated on the same initial state distributions, the STD model shows comparable performance with the additional benefit of the state resolution in the reactant preparation. Starting from specific initial states also leads to a more diverse range of final state distributions, which requires a more expressive neural network compared with DTD. A direct comparison between QCT simulations, the STD model, and the widely used Larsen–Borgnakke (LB) model shows that the STD model is quantitative, whereas the LB model is qualitative at best for rotational distributions P(j′) and fails for vibrational distributions P(v′). As such, the STD model can be well-suited for simulating nonequilibrium high-speed flows, e.g., using the direct simulation Monte Carlo method.

Thermal rates for the C(3P) + O2(3Σ-g) ↔ CO(1Σ+)+ O(1D)/O(3P) reaction are investigated over a wide temperature range based on quasi classical trajectory (QCT) simulations on 3-dimensional, reactive potential energy...