CO2-ice Collisions: A New Experimental Approach

The coagulation of micrometer-sized particles marks the beginning of planet formation. For silicates a comprehensive picture already exists, which describes under which conditions growth can take place and which barriers must be overcome. With increasing distance to the central star volatiles freeze out and the collision dynamics is governed by the properties of the frozen volatiles. We present a novel experiment facility to analyze collisions of CO2 agglomerates consisting of micrometer-sized particles with agglomerate sizes up to 100 μm. Experiments are conducted at temperatures around 100 K with collision velocities up to 3.4 m s−1. Below impact velocities of around 0.1 m s−1 sticking is observed and at collision velocities of 1 m s−1 fragmentation also starts to occur. The experiments show that agglomerates of CO2 ice behave like silicate agglomerates with a comparable grain size distribution. Models developed to describe the collision dynamics of silicate dust can be applied to CO2 ice. This holds for the coefficient of restitution as well as for the threshold conditions for the transitions between sticking, bouncing, or fragmentation.

Vibrational Energy Transfer in CO+N2 Collisions: A Database for V–V and V–T/R Quantum-Classical Rate Coefficients

Knowledge of energy exchange rate constants in inelastic collisions is critically required for accurate characterization and simulation of several processes in gaseous environments, including planetary atmospheres, plasma, combustion, etc. Determination of these rate constants requires accurate potential energy surfaces (PESs) that describe in detail the full interaction region space and the use of collision dynamics methods capable of including the most relevant quantum effects. In this work, we produce an extensive collection of vibration-to-vibration (V–V) and vibration-to-translation/rotation (V–T/R) energy transfer rate coefficients for collisions between CO and N2 molecules using a mixed quantum-classical method and a recently introduced (A. Lombardi, F. Pirani, M. Bartolomei, C. Coletti, and A. Laganà, Frontiers in chemistry, 7, 309 (2019)) analytical PES, critically revised to improve its performance against ab initio and experimental data of different sources. The present database gives a good agreement with available experimental values of V–V rate coefficients and covers an unprecedented number of transitions and a wide range of temperatures. Furthermore, this is the first database of V–T/R rate coefficients for the title collisions. These processes are shown to often be the most probable ones at high temperatures and/or for highly excited molecules, such conditions being relevant in the modeling of hypersonic flows, plasma, and aerospace applications.

Target electron removal in C5+ + H collision

We present target ionization and charge exchange cross sections in a collision between C5+ ion and H atom. We treat the collision dynamics classically using a four-body classical trajectory Monte Carlo (CTMC) and a four-body quasi-classical Monte Carlo (QCTMC) model when the Heisenberg correction term is added to the standard CTMC model via model potential. The calculations were performed in the projectile energy range between 1.0 keV/amu and 10 MeV/amu. We found that the cross sections obtained by the QCTMC model are higher than that of the cross sections calculated by the standard CTMC model and these cross sections are closer to the previous experimental and theoretical data. Moreover, for the case of ionization, we show that the interaction between the projectile and the target electrons plays a dominant role in the enhancement of the cross sections at lower energies.

Bright--Dark Solitons in the Space-Shifted Nonlocal Coupled Nonlinear Schrodinger Equation

Multiple bright-dark soliton solutions in terms of determinants for the space-shifted nonlocal coupled nonlinear Schro¨dinger (CNLS) equation are constructed by using the bilinear (Kadomtsev-Petviashvili) KP hierarchy reduction method. It is found that the bright-dark two-soliton only occur elastic collisions. Upon their amplitudes, the bright two solitons only admit one pattern whose amplitude are equal, and the dark two solitons have three different non-degenerated patterns and two different degenerated patterns. The bright-dark four-soliton is the superposition of the two-soliton pairs and can generated bound-state solitons. The multiple double-pole bright-dark soliton solutions are generated through the long wave limit of the obtained bright-dark soliton solutions, and their collision dynamics are also investigated.PACS 02.30.Jr · 03.75.Lm · 04.20.Jb · 05.45.Yv

Model calculations of φ-meson production in small collision systems

Ultrarelativistic ion collisions provide the unique possibility to study the quark-gluon plasma, a state of matter formed in the universe at the very first moments after the Big Bang. The minimal temperature and baryon density for the quark-gluon plasma formation requires scrutiny, since the signatures of the quark-gluon plasma formation are observed in large systems (such as Au+Au) at s N N = 200 GeV , whereas collective effects in p+p collisions are not revealed. The φ-meson production measurements are considered to be a convenient tool to investigate the collision dynamics, as it is sensitive to the quark-gluon plasma effects. To interpret the nuclear modification effects and to study the process of the possible QGP formation the comparison with different theoretical models predictions is needed. This paper presents the comparison of the obtained experimental results on φ-meson production in small collision systems (p+Al, p+Au) at s N N = 200 GeV to default and string melting versions of the AMPT model and PYTHIA model predictions. The results indicate that the minimal conditions (temperature and baryon density) for a QGP formation may lie in between in p+Al and p+Au collisions.

Neighboring Atom Collisions in Solid-State High Harmonic Generation

High harmonic generation (HHG) from solids shows great application prospects in compact short-wavelength light sources and as a tool for imaging the dynamics in crystals with subnanometer spatial and attosecond temporal resolution. However, the underlying collision dynamics behind solid HHG is still intensively debated and no direct mapping relationship between the collision dynamics with band structure has been built. Here, we show that the electron and its associated hole can be elastically scattered by neighboring atoms when their wavelength approaches the atomic size. We reveal that the elastic scattering of electron/hole from neighboring atoms can dramatically influence the electron recombination with its left-behind hole, which turns out to be the fundamental reason for the anisotropic interband HHG observed recently in bulk crystals. Our findings link the electron/hole backward scattering with Van Hove singularities and forward scattering with critical lines in the band structure and thus build a clear mapping between the band structure and the harmonic spectrum. Our work provides a unifying picture for several seemingly unrelated experimental observations and theoretical predictions, including the anisotropic harmonic emission in MgO, the atomic-like recollision mechanism of solid HHG, and the delocalization of HHG in ZnO. This strongly improved understanding will pave the way for controlling the solid-state HHG and visualizing the structure-dependent electron dynamics in solids.

Preference Parameters for the Calculation of Thermal Conductivity by Multiparticle Collision Dynamics

Calculation of the thermal conductivity of nanofluids by molecular dynamics (MD) is very common. Regrettably, general MD can only be employed to simulate small systems due to the huge computation workload. Instead, the computation workload can be considerably reduced due to the coarse-grained fluid when multiparticle collision dynamics (MPCD) is employed. Hence, such a method can be utilized to simulate a larger system. However, the selection of relevant parameters of MPCD noticeably influences the calculation results. To this end, parameterization investigations for various bin sizes, number densities, time-steps, rotation angles and temperatures are carried out, and the influence of these parameters on the calculation of thermal conductivity are analyzed. Finally, the calculations of thermal conductivity for liquid argon, water and Cu-water nanofluid are performed, and the errors compared to the theoretical values are 3.4%, 1.5% and 1.2%, respectively. This proves that the method proposed in the present work for calculating the thermal conductivity of nanofluids is applicable.