Physics of Ionic and Molecular Interactions

Using a jet spectroscopy molecular beam setup, gas phase electronic spectra of three xylene isomers (para, meta and ortho) have been collected for the neutral monomer species as well as for their clusters with one and two water molecules. Scans at a resolution of ±0.02 nm showed a clear 0–0 transition for each xylene isomer as well as the vibronic progression. The spectra were assigned with the help of Franck–Condon factor PGOPHER simulations from theoretical studies at the CAM-B3LYP/aug-cc-pVDZ level of theory. The vibronic spectra of the xylene⋅H2O and xylene⋅(H2O)2 clusters showed broad features between 36800–38400 cm−1 (260–272 nm) for p- and m-xylene, while the water clusters of o-xylene gave more defined bands. The separation of the vibronic bands in the clusters mirrors the progression of the neutral monomers implying that, for the S1← S0 transition, it is the same vibrational modes that are involved in the monomer as in the clusters with water. Both the separation and the spectral width of the bands can be explained by the calculated differences in geometries of the clusters in the ground and first electronic excited states.

Some internal transport barriers in tokamaks have been related to the vicinity of extrema of the plasma equilibrium profiles. This effect is numerically investigated by considering the guiding-centre trajectories of plasma particles undergoing $\boldsymbol {E}\times \boldsymbol {B}$ drift motion, considering that the electric field has a stationary non-monotonic radial profile and an electrostatic fluctuation. In addition, the equilibrium configuration has a non-monotonic safety factor profile. The numerical integration of the equations of motion yields a symplectic map with shearless barriers. By changing the safety factor profile parameters, the appearance and breakup of these shearless curves are observed. The shearless curve's successive breakup and recovery are explained using concepts from bifurcation theory. We also present bifurcation sequences associated with the creation of multiple shearless curves. Physical consequences of scenarios with multiple shearless curves are discussed.

How are moleculeslinked to each other in complex systems?In aproof-of-concept study, we have developed the method mol2net (https://zenodo.org/record/7025094) to generate and analyze the molecular network of complex astrochemicaldata (from high-resolution Orbitrap MS1 analysis of H2O:CH3OH:NH3 interstellar ice analogs)in a data-driven and unsupervised manner, without any prior knowledgeabout chemical reactions. The molecular network is clustered accordingto the initial NH3 content and unlocked HCN, NH3, and H2O as spatially resolved key transformations. Incomparison with the PubChem database, four subsets were annotated:(i) saturated C-backbone molecules without N, (ii) saturated N-backbonemolecules, (iii) unsaturated C-backbone molecules without N, and (iv)unsaturated N-backbone molecules. These findings were validated withprevious results (e.g., identifying the two major graph componentsas previously described N-poor and N-rich molecular groups) but withadditional information about subclustering, key transformations, andmolecular structures, and thus, the structural characterization oflarge complex organic molecules in interstellar ice analogs has beensignificantly refined.

Context. Formic acid (HCOOH) is the simplest organic carboxylic acid in chemical synthesis and the significant species in interstellar chemistry. HCOOH has been abundantly detected in interstellar ices, dense molecular clouds and star-forming regions. Aims. Laboratory hydrogenation experiments of HCOOH molecules with H atoms were performed with two cryogenic ultra-high vacuum devices on amorphous solid water ices, and highly oriented pyrolytic graphite surfaces. The aim of this work is to study the reactivity of HCOOH molecules with H atoms at low surface temperature 10 K, low surface coverage of one monolayer to three layers, and low H-atom flux of about 3.0 × 1012 molecule cm−2 s−1. Methods. HCOOH and H beams were deposited on cold surfaces held at 10 K, and the condensed films were analyzed by in-situ Reflection Absorption InfraRed Spectroscopy and temperature programmed desorption (TPD) mass spectrometry technique by heating the sample from 10 to 200 K. Results. Using the temperature programmed during exposure desorption technique, we highlight the possible dimerization of HCOOH molecules at low surface temperatures between 10 and 100 K. In our HCOOH+H experiments, we evaluated a consumption of 20–30% of formic acid by comparing the TPD curves at m/z 46 of pure and H-exposed HCOOH ice. Conclusions. The hydrogenation HCOOH+H reaction is efficient at low surface temperatures. The main products identified experimentally are carbon dioxide (CO2) and water (H2O) molecules. CO bearing species CH3OH, and H2CO are also detected mainly on graphite surfaces. A chemical surface reaction route for the HCOOH+H system is proposed to explain the product formation.

Abstract Carbon, hydrogen, nitrogen, oxygen, and sulfur are the main elements involved in the solid-phase chemistry of various astrophysical environments. Among these elements, sulfur chemistry is probably the least well understood. We investigated whether sulfur ion bombardment within simple astrophysical ice analogs (originating from H2O:CH3OH:NH3, 2:1:1) could trigger the formation of complex organosulfur molecules. Over 1100 organosulfur (CHNOS) molecular formulas (12% of all assigned signals) were detected in resulting refractory residues within a broad mass range (from 100 to 900 amu, atomic mass unit). This finding indicates a diverse, rich and active sulfur chemistry that could be relevant for Kuiper Belt objects (KBO) ices, triggered by high-energy ion implantation. The putative presence of organosulfur compounds within KBO ices or on other icy bodies might influence our view on the search of habitability and biosignatures.

The stability of a microtearing mode (MTM) as a function of collisionality is investigated by means of a linear reduced model and numerical simulations using the gyrokinetic code GKW. This study is focused on the role of the electric potential and the magnetic drift, which are potential candidates for explaining the destabilization of MTM observed at low collisionality in some recent gyrokinetic simulations. In the simulations, the magnetic drift and electric potential are found to be destabilizing in the presence of a finite collisionality. This destabilizating role is captured in the analytical calculation, which further highlights the requirement for a finite collisionality.

Abstract A self‐consistent hydrodynamic model for the solar heating‐driven onset of a dust devil vortex is derived and analyzed. The toroidal flows and vertical velocity fields are driven by an instability that arises from the inversion of the mass density stratification produced by solar heating of the sandy surface soil. The nonlinear dynamics in the primary temperature gradient‐driven vertical airflows drives a secondary toroidal vortex flow through a parametric interaction in the nonlinear structures. While an external tangential shear flow may initiate energy transfer to the toroidal vortex flow, the nonlinear interactions dominate the transfer of vertical‐radial flows into a fast toroidal flow. This secondary flow has a vertical vorticity, while the primary thermal gradient‐driven flow produces the toroidal vorticity. Simulations for the complex nonlinear structure are carried out with the passive convection of sand as test particles. Triboelectric charging modeling of the dust is used to estimate the charging of the sand particles. Parameters for a Dust Devil laboratory experiment are proposed considering various working gases and dust particle parameters. The nonlinear dynamics of the toroidal flow driven by the temperature gradient is of generic interest for both neutral gases and plasmas.

The geometric and electronic structures of cold host-guest complex ions of crown ethers (CEs) in the gas phase have been investigated by ultraviolet (UV) fragmentation spectroscopy. As host CEs, we chose 15-crown-5 (15C5), 18-crown-6 (18C6), 24-crown-8 (24C8), and dibenzo-24-crown-8 (DB24C8), and as guests protonated-aniline (aniline·H(+)) and protonated-dibenzylamine (dBAM·H(+)) were chosen. The ions generated by an electrospray ionization (ESI) source were cooled in a quadrupole ion-trap (QIT) using a cryogenic cooler, and UV spectra were obtained by UV photodissociation (UVPD) spectroscopy. UV spectroscopy was complemented by quantum chemical calculations of the most probable complex structures. The UV spectrum of aniline·H(+)·CEs is very sensitive to the symmetry of CEs; aniline·H(+)·18C6 shows a sharp electronic spectrum similar to aniline·H(+), while aniline·H(+)·15C5 shows a very broad structure with poor Franck-Condon factors. In addition, a remarkable cage effect in the fragmentation process after UV excitation was observed in both complex ions. In aniline·H(+)·CE complexes, the cage effect completely removed the dissociation channels of the aniline·H(+) moiety. A large difference in the fragmentation yield between dBAM·H(+)·18C6 and dBAM·H(+)·24C8 was observed due to a large barrier for releasing dBAM·H(+) from the axis of rotaxane in the latter complex.

\nPathways have been disclosed in the past decade, which support the possibility that α-amino acids could have contributed to self-organization processes leading to the emergence of life. It is proposed that the systems chemistry of these simple building blocks may have led to features of self-organization through the realization of protometabolisms based on unidirectional loops involving both peptide formation and breakdown and additional feedback processes. Potential peptide activating agents have been identified. Scenarios of peptide elongation are proposed to account for peptide elongation both at the N-terminus and the C-terminus and new indications that these processes could be involved in symmetry breaking have been provided.\n