The He++H2→HeH++H*(2s,2p) reaction: Study of the s and p contributions in a coincidence-correlation experiment

Non-adiabatic Quantum Dynamics of the Dissociative Charge Transfer He++H2 → He+H+H. Front Chem 2019;7:249. [PMID: 31041310 PMCID: PMC6477054 DOI: 10.3389/fchem.2019.00249]

We present the non-adiabatic, conical-intersection quantum dynamics of the title collision where reactants and products are in the ground electronic states. Initial-state-resolved reaction probabilities, total integral cross sections, and rate constants of two H₂ vibrational states, v₀ = 0 and 1, in the ground rotational state (j₀ = 0) are obtained at collision energies E_coll ≤ 3 eV. We employ the lowest two excited diabatic electronic states of HeH2+ and their electronic coupling, a coupled-channel time-dependent real wavepacket method, and a flux analysis. Both probabilities and cross sections present a few groups of resonances at low E_coll, whose amplitudes decrease with the energy, due to an ion-induced dipole interaction in the entrance channel. At higher E_coll, reaction probabilities and cross sections increase monotonically up to 3 eV, remaining however quite small. When H₂ is in the v₀ = 1 state, the reactivity increases by ~2 orders of magnitude at the lowest energies and by ~1 order at the highest ones. Initial-state resolved rate constants at room temperature are equal to 1.74 × 10⁻¹⁴ and to 1.98 × 10⁻¹² cm³s⁻¹ at v₀ = 0 and 1, respectively. Test calculations for H₂ at j₀ = 1 show that the probabilities can be enhanced by a factor of ~1/3, that is ortho-H₂ seems ~4 times more reactive than para-H₂.

Ion-molecule reactions in 4He droplets: flying nano-cryo-reactors

Ion-molecule reactions are studied inside large (approximately equal to 10(4) atoms) very cold (0.37 K) superfluid (4)He droplets by mass spectrometric detection of the product ions. He+ ions initially formed inside the droplets by electron impact ionization undergo charge transfer with either embedded D(2), N(2), or CH(4). For D(2) this charge transfer process was studied in detail by varying the pickup pressure. For either N(2) or CH(4) the reagent ions were formed by this charge transfer and the reaction pathways of the secondary reactions N(2) (+)+D(2), CH(4) (+)+D(2), and CH(3) (+)+D(2) each with an additionally embedded D(2) molecule were also determined from the pickup pressure dependencies. In several cases, notably He.N(2) (+) and CH(3)D(2) (+) reaction intermediates are observed. The analysis is facilitated by the tendency for molecular ion products to appear without (or with only very few) attached He atoms whereas the atomic ion products usually appear in the mass spectra with several attached He atoms, e.g., He(m).D+ ions with up to m=19.

Three-dimensional moments of molecular property fields

Descriptors that capture certain three-dimensional molecular features and do not require molecular superposition or alignment for the assignment of molecular similarity have recently been proposed and investigated. Among these, moments of molecular features have been utilized in the QSAR of several molecular series. The present work examines certain formal aspects of the use of moment expansions for which the zero-order moment of a property field is nonvanishing. The first-order term of such moment expansion is then dependent upon the origin of expansion, and it is pointed out that expansion about the molecular centroid is descriptive of first-order differences about the property-field mean. For a hydrophobic property field, this first-order term is just the Eisenberg hydrophobic moment. Second-order moments about the centroid can be written as components of the WHIM covariant matrix. Moment expansions are also performed about the property-field center in analogy with expansions about the center of mass. For such expansion, a set of descriptors consisting of moments of the molecular density and of a molecular hydrophobic property field as well as of related quantities are used in a QSAR of the binding of 74 polyhalogenated aromatic molecules to the Ah cystolic receptor. This QSAR has been named CoMMA2 to distinguish it from CoMMA, for which the zero-order moment of the expansion vanishes.