Daniel Peláez

We present the detailed topographical characterisation (stationary points and minimum energy paths connecting them) of the full dimensional (81D) intermolecular potential energy surface associated with the non‐covalent interactions between the NO 2 radical and the pyrene (C 16 H 10 ) molecule. The whole procedure is (quasi) fully automated. We have used our recent algorithm vdW‐TSSCDS as implemented on the freely‐available AutoMekin software package. To this end, a series of inexpensive classical trajectories using forces from a low‐level (semi‐empirical) theory are used to sample the configuration space of the system in the search for candidates to first order saddle points. These guess structures are determined by means of a graph‐theory based algorithm using the concept of adjacency matrix. Low‐level optimizations are followed by re‐optimizations at a final high‐level of theory (DFT and CCSD(T)‐F12 in our case.). The resulting set of stationary points and paths connecting them constitutes the so‐called reaction network. In the case of NO 2 ‐pyrene, this network exhibits four major basins which can be characterized by their point‐group symmetry. A central one, of global C 2 symmetry, comprises the global minimum (as well as all other permutationally related conformers) together with the corresponding C 2 v saddle points connecting them. This central basin is connected to three others of lower C 1 symmetry. The latter can be distinguished by the projection of the position of the NO 2 nitrogen atom on the pyrene plane in combination with the relative orientation of the oxygen pair pointing either inwards, outwards, upwards or downwards.

This work presents systematic comparisons between classical molecular dynamics (cMD) and quantum dynamics (QD) simulations of 15-dimensional and 75-dimensional models in their description of H atom scattering from graphene. We use an experimentally validated full-dimensional neural network potential energy surface of a hydrogen atom interacting with a large cell of graphene containing 24 carbon atoms. For quantum dynamics simulations, we apply Monte Carlo canonical polyadic decomposition to transform the original potential energy surface (PES) into a sum of products form and use the multi-layer multi-configuration time-dependent Hartree method to simulate the quantum scattering of a hydrogen or deuterium atom with an initial kinetic energy of 1.96 or 0.96 eV and an incident angle of 0°, i.e., perpendicular to the graphene surface. The cMD and QD initial conditions have been carefully chosen in order to be as close as possible. Our results show little differences between cMD and QD simulations when the incident energy of the H atom is equal to 1.96 eV. However, a large difference in sticking probability is observed when the incident energy of the H atom is equal to 0.96 eV, indicating the predominance of quantum effects. To the best of our knowledge, our work provides the first benchmark of quantum against classical simulations for a system of this size with a realistic PES. Additionally, new projectors are implemented in the Heidelberg multi-configuration time-dependent Hartree package for the calculation of the atom scattering energy transfer distribution as a function of outgoing angles.

In this work, we have studied the photodissociation of the protonated derivatives of N-nitrosodimethylamine [(CH3)2N–NO] with the CASPT2 method. It is found that only one of the four possible protonated species of the dialkylnitrosamine compound absorbs in the visible region at 453 nm, that is, N-nitrosoammonium ion [(CH3)2NH-NO]+. This species is also the only one whose first singlet excited state is dissociative to directly yield the aminium radical cation [(CH3)2NHN·]+ and nitric oxide. In addition, we have studied the intramolecular proton migration reaction {[(CH3)2N–NOH]+ → [(CH3)2NH–NO]+} both in the ground and excited state (ESIPT/GSIPT); our results indicate that this process is not accessible neither in the ground nor in the first excited state. Furthermore, as a first approximation, MP2/HF calculations on the nitrosamine–acid complex indicate that in acidic solutions of aprotic solvents, only [(CH3)2NH–NO]+ is formed.