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Elementary Processes of Charged Species in Plasma
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
Reaction Eq. (2.99) demonstrates the acidic behavior of nonthermal air plasma. This class of ion-molecular processes consists of very different reactions, which can be subdivided into many groups, including:(A)B+ + C → Α + (C)B+, reactions with a positive ion transfer,A(B+) + C → (B+) + AC, reactions with a neutral transfer,A(B+) + (C)D → (A)D + (C)B+, double exchange reactions,A(B+) + (C)D → AC+ + BD, reconstruction processes.These groups of processes are shown above with positive ions, but similar reactions take place with negative ions. The special feature of the ion-molecular reactions making them very distinctive from regular atom-molecular processes between neutral species can be stated as the following statement: Most Exothermic Ion-Molecular Reactions Have No Activation Energy (V.L. Talrose, 1952). This is because quantum mechanical repulsion between molecules, which provides the activation barrier even in the exothermic reactions of neutrals, can be suppressed by the charge-dipole attraction in ion-molecular reactions. Thus, the rate coefficients are very large and can be found based on the Langevin relations (2.83) and (2.85). Not every Langevin capture leads to the ion-molecular reactions with complicated rearrangement of chemical bonds or to the orbital symmetry and spin-forbidden reactions. For this reason, the pre-exponential Arrhenius factors of the complicated exchange reaction, orbital symmetry, and spin forbidden reactions can be lower than the Langevin rate coefficients (T. Su, M.T. Bowers, 1995). In general, however, the exothermic ion-molecular reactions with rearrangement of chemical bonds are much faster than the corresponding processes between neutrals. This effect is especially important at low temperatures when even small activation barriers can dramatically slow down exothermic reactions. An extensive listing of the ion-molecular reaction rate coefficients is presented in the monograph of L. Virin, R. Dgagaspanian, G. Karachevtsev, V. Potapov, and V. Talrose (1978).
Treating spin-orbit coupling at different levels in equation-of-motion coupled-cluster calculations
Published in Molecular Physics, 2020
Minggang Guo, Zhifan Wang, Fan Wang
Relativistic effects [1–5] are well-known to be important for heavy-element systems and they are divided into scalar-relativistic (SR) effects and spin–orbit coupling (SOC). Treating SOC are usually more demanding than dealing with SR effects since SOC will lower the symmetry and introduce complex algorithm. In fact, SOC is already imperative in phenomena such as fine structure splitting, phosphorescence, spin-forbidden reactions, intersystem crossing as well as EPR g-tensors even if there is no heavy-element in the system. A perturbative treatment of SOC is usually sufficient for such systems. On the other hand, SOC has significant effects on properties of heavy p-block elements [6,7]. This is because the contraction of p1/2 spinors due to SOC is much more pronounced than effects of SOC on the other orbitals. A proper treatment of SOC is required to obtain reliable results for heavy p-block elements. In addition, SOC is more important in open-shell states with nonzero angular momentum than those with zero angular momentum or closed-shell states. An extensive discussion on dealing with SOC effects in quantum chemistry calculations can be found in Ref. [8].