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A full-dimensional global potential energy surface (PES) for the H2 + N2 system is constructed using the permutation invariant polynomial-neural network method, based on high-level ab initio energy points computed at the CCSD(T)-F12a/AVQZ level. To accurately describe the long-range interactions, a multipole expansion parameterized by ab initio data is incorporated into the PES. Quantum close-coupling scattering calculations are reported for rotationally inelastic transitions in H2 + N2 collisions using the full-dimensional PES. Cross sections for rotational excitation of N2 within a rigid rotor model are found to be in excellent agreement with those obtained using a four-dimensional (4D) PES reported by Gomez et al. [Chem. Phys. Lett. 445, 99 (2007)]. Cross sections for pure rotational quenching of H2, as well as quenching of H2 accompanied by rotational excitation of N2, exhibit dense resonance structures. For collision energies above 2.0 cm−1, the results are in close agreement with those obtained using the 4D PES of Gomez et al., including the positions of the sharp resonances. At lower collision energies, however, noticeable differences appear, indicating a strong sensitivity of the resonance features to the PES in this regime. An accurate simulation of energy transfer in collisions between rovibrationally excited H2 and D2 with N2 can now be addressed using the full-dimensional PES reported in this study. 

Full-dimensional quantum scattering calculations are reported for rovibrational transitions in HD+HD collisions using a highly accurate interaction potential for the H2–H2 system. Several near-resonant rovibrational transitions are identified that conserve the overall rotational angular momentum and nearly conserve the internal energy of the collision partners. Key anisotropic terms that drive the rotational transitions and angular momentum partial waves that contribute to low-energy resonant features in the energy dependence of the cross-sections are identified. The computed results agree with total cross-sections reported in previous experimental results, including resonant features in the energy dependence of the cross-section. In particular, low-energy cross-sections show a strong resonant feature associated with an l = 3 partial wave in the incident channel. Rate coefficients for several inelastic rotational and rovibrational transitions are reported for temperatures ranging from 0.1 to 200 K, and they display a maximum between 1 and 10 K, reflecting the important contributions from the l = 3 shape resonance that occurs around 2.5 K. 

Scattering resonances are quantum phenomena arising from the decay of metastable collision complexes trapped by a centrifugal barrier or supported by a closed channel that is coupled to a scattering state. As such, resonances can provide significant insights into the scattering process and serve as a sensitive probe of the interaction potential. In this article, we present a detailed analysis of a cluster of shape resonances associated with the orbital angular momentum L = 5 in the j = 2 → j′ = 0 rotational transition in Ne + D2 collisions for vibrational levels v = 0, 1, and 4. The energies and lifetimes of the resonances arising from different values of the total angular momentum quantum number J were analyzed through numerical fitting of the scattering matrix and employing a one-dimensional model based on an effective potential. We further investigated the sensitivity of the resonances to changes in the alignment of the D2 internuclear axis with respect to the initial relative velocity. Our results show that resonances can be exquisitely controlled by carefully selecting the initial alignment of the D2 molecule. In particular, not only the intensity of the resonance can be modulated but also the shape of the overall resonance profile can be altered, depending on the stereodynamical preferences of the individual resonances that contribute to the cluster. 

A machine learning tool using an ensemble of neural networks is proposed to predict cross sections of rotational transitions in H₂O + H₂O collisions. Bottom right image courtesy of NASA/JPL-Caltech/UMD. 

Resonant scattering of highly vibrationally excited and aligned D2 in cold collisions with Ne has recently been probed experimentally using the Stark-induced adiabatic Raman passage technique [Perreault et al., J. Chem. Phys. 157, 144301 (2022)]. A partial-wave analysis and numerical fitting of the experimental data attributed the measured angular distribution to an l = 2 shape resonance near Ec/kB = 1 K (≈0.7 cm−1). Here, we report the computation of a new potential energy surface for the Ne–H2 interaction suitable for the study of collisions between highly vibrationally excited H2/D2 with Ne as well as quantum scattering calculations of stereodynamics of D2 (v = 4, j = 2) + Ne collisions probing Δj = −2 rotational transition in D2. Our results show that collisions are dominated by a strong l = 5 resonance near 3 K (≈2.09 cm−1) and a weaker l = 6 resonance near 8 K (≈5.56 cm−1) and not an l = 2 resonance, as suggested in the analysis of the experimental data. A reasonable agreement between our calculations and the experiments is obtained only when an artificial energy cutoff is applied to the integral over the collision energy to exclude contributions from the l = 5 resonance while retaining contributions from l = 0, 1, and 2. However, our calculations do not support the claim that the measured angular distributions are dominated by a single l = 2 partial-wave resonance characteristic of orbiting collisions. 

We present a comprehensive quantum mechanical study of stereodynamic control of HD + He and D2 + He collisions that have been probed experimentally by Perreault et al. [J. Phys. Chem. Lett. 13, 10912 (2022)] using Stark-induced adiabatic Raman passage (SARP) techniques. Our calculations utilize a highly accurate full-dimensional H2 + He interaction potential with diagonal Born–Oppenheimer correction appropriate for HD and D2 isotopomers. The results show that rotational quenching of HD from j = 2 → j′ = 0 in v = 2, j = 2 → j′ = 1 in v = 2 and v = 4, and j = 4 → j′ = 3 in v = 4 is dominated by an l = 1 shape resonance located between 0.1 and 1.0 cm−1. For collision energies less than 0.1 cm−1, isotropic scattering prevails. An l = 1 resonance centered around 0.02 cm−1 is also found to dominate the j = 2 → j′ = 0 and j = 4 → j′ = 2 transitions in v = 4 for He–D2 collisions consistent with our prior studies of Δj = −2 transition in He + D2(v = 2, j = 2) collisions. Our analysis does not support the hypothesis of Perreault et al. [J. Phys. Chem. Lett. 13, 10912 (2022)] that a strong l = 2 resonance controls the angular distribution for Δj = −2 transition for both systems. Despite improvements in the development of the potential energy surface, a good agreement with SARP experiments for v = 2 is achieved only when contributions from collision energies less than 1.0 cm−1 were excluded in the computation of velocity averaged differential rate coefficients for both systems. This could be due to some uncertainties in the velocity spread in the experiment that employs co-propagation of the collision partners and possibly, the neglect of transverse velocities in the simulation of the experiment. 

We present an algorithm that combines quantum scattering calculations with probabilistic machine-learning models to predict quantum dynamics rate coefficients for a large number of state-to-state transitions in molecule–molecule collisions much faster than with direct solutions of the Schrödinger equation. By utilizing the predictive power of Gaussian process regression with kernels, optimized to make accurate predictions outside of the input parameter space, the present strategy reduces the computational cost by about 75%, with an accuracy within 5%. Our method uses temperature dependences of rate coefficients for transitions from the isolated states of initial rotational angular momentum j, determined via explicit calculations, to predict the temperature dependences of rate coefficients for other values of j. The approach, demonstrated here for rovibrational transitions of SiO due to thermal collisions with H2, uses different prediction models and is thus adaptive to various time and accuracy requirements. The procedure outlined in this work can be used to extend multiple inelastic molecular collision databases without exponentially large computational resources required for conventional rigorous quantum dynamics calculations.