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The way in which molecules can arrange themselves is at the root of organic chemistry and elucidating the structures present in isomeric mixtures remains a major challenge nowadays. A tantalizing question for chemists is how molecules transform from one structural configuration to another one. This review introduces in details a technique—tunable photoionization chemical monitoring—that couples tandem mass spectrometry and photoionization enabling to answer the two aforementioned questions for molecular ions. It is based on tracking reactivity changes in bimolecular ion–molecule reactions as a function of the internal energy of the ions. This is illustrated with (i) the structural elucidation of ortho‐benzyne distonic cation within a C 6H4+ population and (ii) the tracking of the isomerization from azulene radical cation as it gets gradually energized to naphthalene cation. In both cases, charge transfer reactions have been primarily used because of their universality. Finally, a state‐of‐the‐art of the TPI‐CM technique using the CERISES mass spectrometer is given, indicating current limitations as well as prospects of improvement. [ABSTRACT FROM AUTHOR]

New highly exothermic formation pathways incorporating both thermodynamic and kinetic control for the newly astronomically detected H _2 CNCN molecule are paired with extremely accurate quantum chemical rovibrational spectroscopic computations. The reactions between astronomically known CH _2 CN/CH _2 CCH + HNCN follow effectively identical pathways and proceed through stable intermediates and over deeply submerged transition states to form H _2 CNCN and HCN/HCCH coproducts. Similarly, the reaction between CH _2 CN and NCN ^− can also form H _2 CNCN, although this pathway first requires the initial formation of NCN ^− , which is currently undetected in space, via HNCN + CN ^− . This two-step mechanism uses the highly abundant CN ^− as the catalyst. Incredibly accurate quantum chemical spectroscopic data are reported for all reactants and products of these reactions, with errors between experimental values and the computations herein on the order of 0.1% or less. Anharmonic vibrational frequencies and intensities are also reported in order to guide experimental and observational searches for these molecules that have mostly been detected in the radio but may now be detectable via JWST.

Interstellar Boundary Explorer (IBEX) observations of energetic neutral atom (ENA) fluxes from the heliosphere have greatly enriched our understanding of the interaction of the solar wind (SW) with the local interstellar medium (LISM). However, there has been recent controversy surrounding the inability of most ENA models to produce as high an intensity of ∼0.5–6 keV ENAs as IBEX observes at 1 au, especially as a function of time. In our previous study (E. J. Zirnstein et al.), we introduced a new model that utilizes a data-driven magnetohydrodynamic simulation of the SW–LISM interaction to propagate pickup ions through the heliosheath (HS) after they are nonadiabatically heated at the heliospheric termination shock. E. J. Zirnstein et al. only simulated and analyzed IBEX observations from the direction of Voyager 2. In this study, we expand our model to include fluxes from the direction of Voyager 1, as well as in the low-latitude part (middle) of the ribbon (10° below the ecliptic plane). We show that the model results at Voyager 1 are consistent with E. J. Zirnstein et al.’s results at Voyager 2 in terms of a secondary ENA source contribution of ≲20% from both directions. Our results in the middle of the ribbon also reproduce the data, when including a time-dependent secondary ENA source. Finally, we demonstrate with our simulation that three large pressure waves likely merged in the VLISM and were observed by Voyager 1 as “pf2,” while at least one of the wave’s effects in the HS was observed by IBEX as a brief enhancement in ENA flux in early 2016.

We present the temperature-dependent reaction rate coefficients of CN ^− and C _3 N ^− with atomic hydrogen in the temperature range from 7 to 290 K, measured in a 16-pole radio-frequency ion trap. The rate of C _3 N ^− with H steadily increases toward lower temperatures, while the rate coefficients for the CN ^− + H system show a sudden change around 160 K. Fits to the data were performed to determine temperature-dependent reaction rate coefficients. The fits reveal a rate coefficient of $4.1{(3)\times {10}^{-10}(T/300)}^{-0.31(6)}$ cm ^3 s ^−1 for C _3 N ^− + H. For CN ^− , we determined a rate coefficient for the temperature regime below 160 K of $3.2{(4)\times {10}^{-10}(T/300)}^{-0.31(11)}$ cm ^3 s ^−1 . Given our present results, higher rate coefficients than previously reported must be assumed for the modeling of cold interstellar environments involving these H atom reactions.

Interstellar neutral (ISN) helium atoms penetrating the heliosphere are used to find the flow velocity and temperature of the very local interstellar medium near the heliosphere. Recently, it was found that, in addition to charge exchange collisions, elastic collisions contribute to the filtration of these atoms outside the heliopause. Momentum exchange between colliding particles related to their angular scattering modifies the properties of the primary and secondary ISN helium populations before the atoms enter the heliosphere. Here, we calculate the transport of ISN helium atoms using plasma and neutral flows from a global three-dimensional heliosphere model. We confirm earlier results based on one-dimensional calculations that the primary population is slowed down and heated by the momentum exchange. Moreover, accounting for momentum exchange in charge exchange collisions results in a faster and warmer secondary population. The paper presents how the velocity and density of these populations vary over the entrance position to the heliosphere. We point out that Maxwell distributions cannot correctly describe these populations. Finally, we calculate the expected Interstellar Boundary Explorer (IBEX) count rates and show that the filtration processes change them significantly. Consequently, future studies of IBEX or Interstellar Mapping and Acceleration Probe (IMAP) observations of ISN atoms should account for these processes. [ABSTRACT FROM AUTHOR]

We have performed experimental investigations of methanol formation via the reactions of low-energy CH _3 ^+ ions with an amorphous solid water (ASW) surface at ∼10 K. A newly developed experimental apparatus enabled irradiation of the ASW surface by several eV ions and detection of trace amounts of reaction products on the surface. It was found that methanol molecules were produced by low-energy CH _3 ^+ irradiation of the ASW surface and that hydroxy groups in the produced methanol originated from water molecules in the ASW, as predicted in a previous theoretical study. Little temperature dependence of the observed methanol intensity is apparent in the temperature range 12–60 K. Ab initio molecular dynamics simulations under constant-temperature conditions of 10 K suggested that this reaction spontaneously produced a methanol molecule and an H _3 O ^+ ion, regardless of the contact point of CH _3 ^+ on the ASW surface. We have performed a simulation with an astrochemical model under molecular-cloud conditions, where the reaction between CH _3 ^+ and H _2 O ice, leading to methanol formation, was included. We found that the impact of the reaction on methanol abundance was limited only at the edge of the molecular cloud (

The new Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics (Heidelberg, Germany) has recently become operational. One of the main research areas foreseen for this unique facility is astrochemical studies with cold molecular ions. The spontaneous radiative cooling of the prototype interstellar molecule CH+ to its lowest rotational states has been demonstrated by photodissociation spectroscopy, paving the way for experiments under true interstellar conditions. To this end, a low-energy electron cooler and a neutral atom beam set-up for merged beams studies have been constructed. These experiments have the potential to provide energy-resolved rate coefficients for fundamental astrochemical processes involving state-selected molecular ions. The main target reactions include some of the key processes of interstellar chemistry, such as the electron recombination of H3+, charge exchange between H+2 and H, or the formation of CH+ in collisions of triatomic hydrogen ions and C atoms. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'. [ABSTRACT FROM AUTHOR]

This review is concerned with the formation of molecules in the interstellar medium (ISM), which is composed mainly of regions of gas and dust known as interstellar clouds, ranging in size from a few to 100’s of light years in extent. Upwards of 200 different molecules have been observed spectroscopically in these objects, with a significant fraction of them ‘large’ by astronomical standards; i.e. containing six or more atoms. Interstellar clouds are of interest to chemists because of the exotic molecules and chemistry that occur in these sources, while they are of interest to astronomers because these clouds are the only known birthplaces of new stars and extrasolar planets. The formation of stars and planets from portions of dense interstellar clouds is a complex evolutionary process with multiple stages dependent upon the mass of the collapsing object. For low-mass stars such as our sun, the process is reasonably well understood and proceeds through the following intermediate stages: cold dense cores, pre-stellar cores, hot cores, and protoplanetary discs. For high-mass stars, the process is significantly less well understood because these objects are rare and are formed through evolutionary stages that are short in duration, at least astronomically speaking. Molecules are found in all of these stages, in the gas phase and often in the solid phase, with the chemistry dependent upon the physical conditions and their history. Indeed, the many molecules detected have helped significantly to unravel much of the complexity involved in stellar and planetary formation. This review is divided into sections in which, following an introduction, we discuss the different types of chemical reactions that synthesise large molecules, starting with cold dense cores of temperature 10 K and gas density, and proceeding through the various stages of low-mass star formation through protoplanetary discs. Several other types of sources are discussed briefly. We then review some recent progress that has occurred within the last several years in improving our knowledge of the chemistry in this fast-growing and rapidly evolving field of research. We end with a brief discussion of the detailed chemical simulations employed to follow the chemistry in the various sources in the ISM. [ABSTRACT FROM AUTHOR]

In this study we report theoretical and experimental evidence for the formation of ionic products by the ion-neutral reaction of C 2 H 2 N + with C 2 H 6 . Our investigations consist of laboratory measurements using a guided ion beam mass spectrometer together with complementary ab initio quantum chemical computations, at the MP2/6-311++G(d,p) level of theory, in order to elucidate the energetics and geometries of the intermediates and transition states that are involved in the production of the observed product ions. This study also provides insights on the isomeric nature of the observed product ions, their formation pathways together with collision energy and pressure dependences. The experimental data agrees well with the predictions of the ab initio calculations. Despite data provides evidence for the occurrence of C 2 H 5 + as the most salient product ion, the production of CH 3 + , C 2 H 3 + , C 3 H 5 + , C 3 H 7 + and C 2 H 4 N + is also evident. A reaction scheme was proposed to elucidate the mechanisms responsible for the formation of the observed product ions. These processes might be intermediate steps in the generation of long chain carbon and nitrogen-bearing compounds in Titan's ionosphere, the interstellar medium or circumstellar envelopes. [ABSTRACT FROM AUTHOR]

Effect of nanosecond lasers on the methane dissociation is experimentally studied by using three different laser wavelengths at 248 nm, 355 nm and 532 nm. C 2 H 2 generation is measured as a major reaction product in experiments and the energy consumptions in production of this component are measured as 5.8 MJ/mol, 3.1 MJ/mol and 69.0 MJ/mol, for 355 nm, 532 nm and 248 nm wavelengths, respectively. The mechanism of conversion and production of new stable hydrocarbons is also theoretically investigated. It is found that in theoretical calculations, the ion-molecule reactions should be included and this leads to a unique approach in proper explanation of the experimental measurements. [ABSTRACT FROM AUTHOR]

Structural rearrangements in ions are essential for understanding the composition and evolution of energetic and chemically active environments. This study explores the interconversion routes for simple polycyclic aromatic hydrocarbons, namely naphthalene and azulene radical cations (C 10 H 8 + ), by combining mass spectrometry and vacuum ultraviolet tunable synchrotron radiation through the chemical monitoring technique. Products of ion-molecule reactions are used to probe C 10 H 8 + structures that are formed as a function of their internal energies. Isomerisation from azulene radical cation towards naphthalene radical cation in a timescale faster than 80 μs was monitored, whereas no reverse isomerisation was observed in the same time window. When energising C 10 H 8 + with more than 6 eV, the reactivity of C 10 H 8 + unveils the formation of a new isomeric group with a contrasted reactivity compared with naphthalene and azulene cations. We tentatively assigned these structures to phenylvinylacetylene cations., (© 2022 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

Aromatic hydrocarbons (AHs) and their derivatives have been suggested as the building blocks of interstellar dust grains and are responsible for the evolution of astrobiological molecules via surface reactions in space. Gas-phase studies of molecules and ions known to exist in space are crucial to understand relevant ion–molecule reactions and the generation of new species. Reactions catalyzed by large species such as AHs remain relatively unexplored. Our computational studies focus on the energetics and reaction mechanisms of the formation of representative molecules (i.e., hydrogen peroxide, acetamide, and amino acetonitrile) that are critical for the origin of water and amino acids in the universe. Calculations have been carried out using Gaussian 09 to obtain the structures, energetics, and reaction mechanisms to investigate the formation of hydrogen peroxide (H 2 O 2 ), acetamide (CH 3 C(O)NH 2 ), and amino acetonitrile (NH 2 CH 2 CN). Our results suggest that there are energetically accessible reaction pathways leading to the formation of these molecules through species which have been discovered in the interstellar medium (ISM). Ionized benzene and polycyclic aromatic hydrocarbons (PAHs) can act as catalysts to facilitate the formation of astromolecules. The theoretical studies can enhance our understanding of ion–molecule reactions that are relevant to the formation of important astromolecules in the gas phase, and provide a new way to investigate the formation of polyatomic molecules on surfaces of dust grains such as large PAHs. [ABSTRACT FROM AUTHOR]