Neutral Dissociation of Pyridine Evoked by Irradiation of Ionized Atomic and Molecular Hydrogen Beams

The interactions of ions with molecules and the determination of their dissociation patterns are challenging endeavors of fundamental importance for theoretical and experimental science. In particular, the investigations on bond-breaking and new bond-forming processes triggered by the ionic impact may shed light on the stellar wind interaction with interstellar media, ionic beam irradiations of the living cells, ion-track nanotechnology, radiation hardness analysis of materials, and focused ion beam etching, deposition, and lithography. Due to its vital role in the natural environment, the pyridine molecule has become the subject of both basic and applied research in recent years. Therefore, dissociation of the gas phase pyridine (C5H5N) into neutral excited atomic and molecular fragments following protons (H+) and dihydrogen cations (H2+) impact has been investigated experimentally in the 5–1000 eV energy range. The collision-induced emission spectroscopy has been exploited to detect luminescence in the wavelength range from 190 to 520 nm at the different kinetic energies of both cations. High-resolution optical fragmentation spectra reveal emission bands due to the CH(A2Δ → X2Πr; B2Σ+ → X2Πr; C2Σ+ → X2Πr) and CN(B2Σ+ → X2Σ+) transitions as well as atomic H and C lines. Their spectral line shapes and qualitative band intensities are examined in detail. The analysis shows that the H2+ irradiation enhances pyridine ring fragmentation and creates various fragments more pronounced than H+ cations. The plausible collisional processes and fragmentation pathways leading to the identified products are discussed and compared with the latest results obtained in cation-induced fragmentation of pyridine.

Quantum Dynamics of Rotational Transitions in CN (X2Σ+) by H+ Collisions

Collisional cross-sections of inelastic rotational excitations of CN in its ground electronic state (X2Σ+) by H+ scattering are studied by the exact quantum mechanical close-coupling (CC) method at very low collision energies (0–600 cm−1) relevant to interstellar atmospheres. Ab initio rigid rotor potential energy surface computed at MRCI/cc-pVTZ level of accuracy has been employed. Rate coefficients for the rotational excitations have also been calculated. The obtained results are compared with previous theoretical calculations and analyzed whether proton collisions could be significant sources for rotationally excited CN as a possible source for cosmic microwave background of about 3 K from the interstellar media.

A Decade and a Half of Fast Radio Burst Observations

Fast radio bursts (FRBs) have a story which has been told and retold many times over the past few years as they have sparked excitement and controversy since their pioneering discovery in 2007. The FRB class encompasses a number of microsecond- to millisecond-duration pulses occurring at Galactic to cosmological distances with energies spanning about 8 orders of magnitude. While most FRBs have been observed as singular events, a small fraction of them have been observed to repeat over various timescales leading to an apparent dichotomy in the population. ∼50 unique progenitor theories have been proposed, but no consensus has emerged for their origin(s). However, with the discovery of an FRB-like pulse from the Galactic magnetar SGR J1935+2154, magnetar engine models are the current leading theory. Overall, FRB pulses exhibit unique characteristics allowing us to probe line-of-sight magnetic field strengths, inhomogeneities in the intergalactic/interstellar media, and plasma turbulence through an assortment of extragalactic and cosmological propagation effects. Consequently, they are formidable tools to study the Universe. This review follows the progress of the field between 2007 and 2020 and presents the science highlights of the radio observations.

A geostatistical analysis of multiscale metallicity variations in galaxies [I]: Introduction and comparison of high-resolution metallicity maps to an analytic metal transport model

Thanks to recent advances in integral field spectroscopy (IFS), modern surveys of nearby galaxies are capable of resolving metallicity maps of H ii regions down to scales of ∼50pc. However, statistical analysis of these metallicity maps has seldom gone beyond fitting basic linear regressions and comparing parameters to global galaxy properties. In this paper (the first of a series), we introduce techniques from spatial statistics that are well suited for detailed analysis of both small- and large-scale metallicity variations within the interstellar media (ISMs) of local galaxies. As a first application, we compare the observed structure of small-scale metallicity fluctuations within 7 local galaxies observed by the PHANGS collaboration to predictions from a stochastic, physically motivated, analytical model developed by Krumholz & Ting. We show that while the theoretical model underestimates the amount of correlated scatter in the galactic metallicity distributions by 3 − 4 orders of magnitude, it provides good estimates of the physical scale of metallicity correlations. We conclude that the ISM of local spiral galaxies is far from homogeneous, with regions of size ∼1 kpc showing significant departures from the mean metallicity at each galactocentric radius.

Reaction mechanisms of C(3PJ) and C+(2PJ) with benzene in the interstellar medium from quantum mechanical molecular dynamics simulations

While spectroscopic data on small hydrocarbons in interstellar media along with crossed molecular beam experiments have provided a wealth of information on astrochemical species, much of the underlying mechanistic pathways of their formation remain elusive.

Evolving supernova remnants in multiphase interstellar media

ABSTRACT We performed three-dimensional magnetohydrodynamic simulations to study the evolution of a supernova remnant (SNR) in a turbulent neutral atomic interstellar medium. The media used as background shares characteristics with the Solar neighbourhood and the SNR has mass and energy similar to those of a Type Ia object. Our initial conditions consist of dense clouds in a diluted medium, with the main difference between simulations being the average magnitude of the magnetic field. We measured amplifications of the magnetic energy of up to 34 ${{\rm per\ cent}}$, and we generated synthetic maps that illustrate how the same object can show different apparent geometries and physical properties when observed through different lines of sight.

Origin of Terrestrial Bioorganic Homochirality and Symmetry Breaking in the Universe

The origin of terrestrial bioorganic homochirality is one of the most important and unresolved problems in the study of chemical evolution prior to the origin of terrestrial life. One hypothesis advocated in the context of astrobiology is that polarized quantum radiation in space, such as circularly polarized photons or spin-polarized leptons, induced asymmetric chemical and physical conditions in the primitive interstellar media (the cosmic scenario). Another advocated hypothesis in the context of symmetry breaking in the universe is that the bioorganic asymmetry is intrinsically derived from the chiral asymmetric properties of elementary particles, that is, parity violation in the weak interaction (the intrinsic scenario). In this paper, the features of these two scenarios are discussed and approaches to validate them are reviewed.