Crystallization of ion clouds in octupole traps: structural transitions, core melting, and scaling laws

International audienceThe stable structures and melting properties of ion clouds in isotropic octupole traps are investigated using a combination of semi-analytical and numerical models, with a particular emphasis at finite size scaling effects. Small-size clouds are found to be hollow and arranged in shells corresponding approximately to the solutions of the Thomson problem. The shell structure is lost in clusters containing more than a few thousands of ions, the inner parts of the cloud becoming soft and amorphous. While melting is triggered in the core shells, the melting temperature unexpectedly follows the rule expected for three-dimensional dense particles, with a depression scaling linearly with the inverse radius

The CH-3Σ+ anion: inelastic rate coefficients from collisions with he at interstellar conditions

We present accurate ab initio calculations on several properties of a gas-phase system of interest in the interstellar medium (ISM), where the title molecular anion has been often surmised but not yet confirmed by observations. The CH-3Σ+ constitutes the smallest term in the series of longer anionic polyynes which have been observed in the ISM (e.g., C4H- and several others). Hence, its dynamical behavior in collision with He atoms, one of the most abundant atoms in that environment, can provide quantitative indicators on the changes which can occur in the rotational state population of the title anion when driven by this collision dynamics. We therefore report an accurate evaluation of the full potential energy surface (PES) which acts between the molecular anion in its ground vibrational state and the He atom. The relevant inelastic scattering cross sections and the corresponding inelastic rate coefficients are then computed within a quantum treatment of the collisions. We find that the fairly small values of the final inelastic rate coefficients indicate state-changing processes by collisions to be inefficient paths for modifying the rotational state populations of this anion and therefore to aid its possible observation from direct radiative emission in the microwave regio

Collision-induced state-changing rate coefficients for cyanogen backbones NCN 3Σ− and CNN 3Σ− in astrophysical environments

We report quantum calculations involving the dynamics of rotational energy-transfer processes, by collision with He atoms in interstellar environments, of the title molecular species which share the presence of the CN backbone and are considered of importance in those environments. The latter structural feature is taken to be especially relevant for prebiotic chemistry and for its possible role in the processing of the heterocyclic rings of RNA and DNA nucleobases in the interstellar space. We carry out ab initio calculations of their interaction potentials with He atoms and further obtain the state-to-state rotationally inelastic cross sections and rate coefficients over the relevant range of temperatures. The similarities and differences between such species and other similar partners which have been already detected are analyzed and discussed for their significance on internal state populations in interstellar space for the two title molecular radicalsFAG acknowledges the support of the Computing Center of Innsbruck University where part of the present calculations were carried out. L. G.-S. acknowledges the financial support by Ministerio de Ciencia e Innovacio´n (Spain) MCIN/AEI/10.13039/ 501100011033 (Ref. PID2020-113147GA-I00 and PID2021- 122839NB-I00) and C.S-S. further acknowledges the financial support by Ministerio de Ciencia e Innovacio´n (Spain) Ref. PID2021-122549NB-C2

Algebraic approaches to eigenvalue equations: The Wronskian method

A recently proposed method for the solution of eigenvalue equations is applied to two different model potentials. Considerable improvements are observed if the algebraic requirements of the Wronskian method are enforced over a region instead of at a single point.Publisher's Versio

Coating of C60 by para-H2 and ortho-D2 : revisiting the solvation shell—CMMSE

International audienc

Thermochromism in oligothiophenes: The role of the internal rotation

The relation between thermochromism in polythiophenes and the internal rotation is studied by density-functional theory (DFT). For head-to-tail methyl-substituted thiophenes, rotational potential maps of dimer and trimer are calculated. With time-dependent-DFT methodology the absorption spectra of these oligomers in UV-vis region are calculated as functions of the torsional angles. Theoretical temperature-dependent UV-vis spectra are generated from the distribution of torsional angles. The results show that the internal rotation alone is not sufficient to explain the mechanism of thermochromism