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Molecular ions are relatively cold in the E region ionosphere; however, they can upwell to the magnetosphere during geomagnetically active times. Resonance between electrostatic ion cyclotron (EIC) waves is a potential pathway to energize molecular ions. In this work, the E region ionospheric plasma was modeled in the laboratory, and EIC waves were excited by a nonuniform field‐aligned current. The EIC wave was excited even when the ion neutral collision frequency is much higher than the ion cyclotron frequency, and the fundamental frequency was observed to be below the ion cyclotron frequency. In addition, the wave dispersion of the collisional EIC wave was calculated, which shows a consistent trend with experimental results as the collisions increasing. Therefore, this work suggests that EIC waves can be excited in the E region ionospheric‐like plasma, which can support the explanation of the energization of molecular ions in the E region ionosphere. Plain Language Summary: Spacecraft observed the presence of molecular ions in the topside ionosphere (600–1,000 km) and the magnetosphere during geomagnetically active times, and the potential mechanisms responsible for the acceleration of these molecular ions are still not fully understood. The resonance between electrostatic ion cyclotron (EIC) waves and molecular ions is a potential pathway to energize the molecular ions. However, most previous works on EIC waves were studied in collisionless plasma similar to the magnetospheric plasma, which is different from the E region ionospheric plasma. A typical characteristic of E region ionospheric plasma is the partially ionized effect, which introduces new physical processes that do not occur in collisionless plasmas. In this work, strong collisions that occurred in the E region ionosphere were simulated in the laboratory, and the current‐driven electrostatic ion cyclotron waves were observed in the modeled ionosphere. It is found that electrostatic ion cyclotron waves can be generated in the E region ionospheric‐like plasma. This work provides solid experimental evidence that electrostatic ion cyclotron instability can exist in weakly ionized plasmas of the E region ionosphere, and can be applied to explain the transverse ion heating of bulk ions in the bottomside ionosphere. Key Points: The E region ionospheric‐like collisional plasma was modeled in the laboratoryEIC waves were excited by field aligned current in the ionospheric‐like plasmaThis work can be applied to explain the energization of molecular ions in the E region ionosphere [ABSTRACT FROM AUTHOR]

Abstract Molecular ions are relatively cold in the E region ionosphere; however, they can upwell to the magnetosphere during geomagnetically active times. Resonance between electrostatic ion cyclotron (EIC) waves is a potential pathway to energize molecular ions. In this work, the E region ionospheric plasma was modeled in the laboratory, and EIC waves were excited by a nonuniform field‐aligned current. The EIC wave was excited even when the ion neutral collision frequency is much higher than the ion cyclotron frequency, and the fundamental frequency was observed to be below the ion cyclotron frequency. In addition, the wave dispersion of the collisional EIC wave was calculated, which shows a consistent trend with experimental results as the collisions increasing. Therefore, this work suggests that EIC waves can be excited in the E region ionospheric‐like plasma, which can support the explanation of the energization of molecular ions in the E region ionosphere.

Atmospheric pressure field desorption (APFD) mass spectrometry (MS) has recently been explored as a new contribution to the field of ambient desorption/ionization (ADI). Depending on the selected polarity applied to the field emitter, ionic and polar analytes were demonstrated to deliver positive as well as negative ions. Whereas this recent study solely reported on the formation of even-electron ions of either polarity, the present work on APFD-MS demonstrates the abundant formation of positive molecular ions, M+•, from polycyclic aromatic compounds. Molecular ions were formed on and desorbed from standard 13-µm activated tungsten wire emitters at atmospheric pressure. The commercial field emitters were positioned at about 2 mm distance in front of the atmospheric pressure interface of a Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer and the entrance electrode of the interface was set to –4.5 to –5.5 kV with respect to the emitter. Emitter-disrupting electric discharges did normally not occur under these conditions. The electric field strengths achieved at the dendritic microneedles were sufficient to allow for the abundant formation of M+• ions of various polycyclic aromatic compounds such as benzo[a]pyrene, anthracene, fluoranthene, 1,1,4,4-tetraphenyl-butadiene, and 1-aza-[6]helicene. In case of the extremely basic 1-aza-[6]helicene protonation strongly competed with molecular ion formation and tended to suppress the field ionization process. All molecular ion compositions were assured by accurate mass-based formula assignments. [ABSTRACT FROM AUTHOR]

Recently, the upper bounds on the static time-reversal (T) and spatial parity (P)-violating electron electric dipole moment (eEDM) and dimensionless constant, characterizing the strength of the T , P -violating scalar–pseudoscalar nucleus–electron interaction, have been updated in the JILA experiment using the HfF+ cations. We considered two other sources of the T , P -violation in HfF+–axion-like-particle (ALP)-mediated scalar–pseudoscalar electron–electron and nucleus–electron interactions. To estimate the magnitude of effects, induced by such interactions in HfF+ we have developed and applied a method which implies the direct use of the ab initio relativistic coupled cluster theory to calculate molecular parameters that characterize the interactions. Using these parameters, we showed that an order of magnitude updated laboratory constraints on the ALP-mediated electron–electron and nucleus–electron interactions can be derived from the experimental data on T , P -violating effects in HfF+ for a wide range of ALP masses. [ABSTRACT FROM AUTHOR]

Precision spectroscopy has been the driving force for progress of our physical understanding and still is a promising tool for the investigation of new physics. Molecules offer transitions which allow tests that are not possible in atomic systems. However, usually precision spectroscopy of molecules is challenging due to the lack of cycling transitions for state preparation and state detection. For molecular ions, this obstacle can be overcome by quantum logic spectroscopy, where dissipation for state preparation and detection is provided by a co-trapped atomic ion exploiting the shared eigenstates of motion. Here, we propose a full quantum logic spectroscopy scheme for molecular oxygen ions and theoretically investigate the feasibility of quantum logic-assisted state detection and preparation. Furthermore, we provide coupling rates for a direct single-photon quadrupole excitation of a vibrational overtone transition that can serve as a sensitive reference for tests of a possible variation of the proton-to-electron mass ratio.

The importance of the symmetric as well as non-symmetric ion-atom absorption processes in broad spectral region within a model of solar photosphere and also within the corresponding sunspot models, has been previously emphasized. This motivated us to study the photo-association, charge-exchange and photo-dissociation absorption processes in the cases of non-symmetric and symmetric systems involving hydrogen and potassium atoms, ions, molecules and molecular-ions. We have calculated the data for molecules and molecular state characterizations needed for current computation. We determined the partial and average cross-sections and corresponding spectral absorption rate coefficients, as the functions of wavelengths, and temperatures (100 nm ⩽ λ ⩽ 1000 nm, 400 K ⩽ T ⩽ 10 000 K). Our calculations are performed for conditions that exist in different layers of weakly ionized stellar atmospheres. The obtained data are potentially of high impact and may have broad further applications, e.g., for modelling of laboratory plasmas and various astrophysical objects including geocosmical ones. [ABSTRACT FROM AUTHOR]

In this study, the processes of photo-dissociation in the cases of symmetric and strongly non-symmetric systems which involve hydrogen and potassium are investigated. The aim of this study was to calculate data for those small molecules and molecular state characterizations as well as to obtain the corresponding partial and average cross-sections. Moreover, the corresponding spectral absorption rate coefficients for symmetric and strongly non-symmetric cases i.e. for K 2 + and KH+ cases are given in tables as a function of temperatures and wavelengths allowing potential modeling. The current research and presented results can be of interest for astrophysical plasma research and laboratory plasma investigation. [ABSTRACT FROM AUTHOR]

In this manuscript, the chemi-ionization (CI) processes in atom - Rydberg atom collisions are examined. We obtained the cross-sections, as well as rate coefficients for CI processes in potassium and sodium collisions for principal quantum numbers 5 ⩽ n ⩽ 25 in the 500 K ⩽ T ⩽ 1500 K temperature region. The presented data could be useful for the improvement of analysis and modelling of weakly ionized layers of different atmospheres and cosmic objects where these and other CI processes could change excited state populations and the free electron density, consequently affecting the optical characteristics. [ABSTRACT FROM AUTHOR]

Recently, the upper bounds on the static time-reversal (\({\mathcal{T}}\)) and spatial parity (\({\mathcal{P}}\))-violating electron electric dipole moment (eEDM) and dimensionless constant, characterizing the strength of the \({\mathcal{T}}\),\({\mathcal{P}}\)-violating scalar–pseudoscalar nucleus–electron interaction, have been updated in the JILA experiment using the HfF+ cations. We considered two other sources of the \({\mathcal{T}}\),\({\mathcal{P}}\)-violation in HfF+–axion-like-particle (ALP)-mediated scalar–pseudoscalar electron–electron and nucleus–electron interactions. To estimate the magnitude of effects, induced by such interactions in HfF+ we have developed and applied a method which implies the direct use of the ab initio relativistic coupled cluster theory to calculate molecular parameters that characterize the interactions. Using these parameters, we showed that an order of magnitude updated laboratory constraints on the ALP-mediated electron–electron and nucleus–electron interactions can be derived from the experimental data on \({\mathcal{T}}\),\({\mathcal{P}}\)-violating effects in HfF+ for a wide range of ALP masses.

Ionospheric molecular ions, such as NO+, N2+ and O2+, are gravitationally bound, and are expected to undergo recombination to form a pair of neutral atoms, due to short dissociative recombination lifetime. Therefore, they are expected to be relatively cold in the Earth’s atmosphere, compared with light ions such as H+ and He+, or even heavier ions such as N+ or O+. However, several spacecraft missions observed their presence in the high-altitude ionosphere and the magnetosphere, predominantly during the geomagnetically active times. This hints to the possibility that molecular ions have the ability to acquire sufficient energy in a very short time, and can be used as tracers of mass differentiated vertical transport to understand the mechanisms responsible for “fast ionospheric outflow.” In this letter, we review the observational data sets that reported on the abundances of molecular ions in the Earth’s magnetosphere-ionosphere system, starting from their first observations by the Sputnik III mission, to the current Arase (ERG) satellite and Enhanced Polar Outflow Probe (e-POP) missions. The available data suggests that molecular ions are quite abundant in the lower atmosphere at all times, but are only seen in the high-altitude ionosphere and magnetosphere during the times of increased geomagnetic activity.

Abstract Molecular ions in the magnetosphere can be a tracer of fast ion outflows from the deep ionosphere. Statistical properties of molecular ions (O2+/NO+/N2+) in the ring current are investigated based on ion composition measurements (

I present a novel scheme for producing cold (magnetically trappable) atomic hydrogen, based on threshold photodissociation of the BaH ^+ molecular ion. BaH ^+ can be sympathetically cooled using laser cooled Ba ^+ in an ion trap, before it is photodissociated on the single photon A ^1 Σ ^+ ← X ^1 Σ ^+ transition. The small mass ratio between Ba ^+ and BaH ^+ ensures a strong overlap within the ion trap for sympathetic cooling, while the large mass ratio between BaH ^+ and H means that the released hydrogen can be up to 139 times colder than the parent molecular ions. I examine the hydrogen production rate, and describe how the trap dynamics and photodissociation laser detuning influence the achievable energies. The low infrastructure costs and the ion trap nature of the scheme make it suitable for loading hydrogen into an antihydrogen experiment. This would support a direct matter–antimatter comparison, which could provide important clues as to why our Universe contains so little antimatter.

Polarizable force fields are emerging as a more accurate alternative to additive force fields in terms of modeling and simulations of a variety of chemicals including biomolecules. Explicit treatment of induced polarization in charged species such as phosphates and sulfates offers the potential for achieving an improved atomistic understanding of the physical forces driving their interactions with their environments. To help achieve this, in this study we present balanced Drude polarizable force field parameters for molecular ions including phosphates, sulfates, sulfamates, and oxides. Better balance was primarily achieved in the relative values of minimum interaction energies and distances of the anionic model compounds with water at the Drude and quantum mechanical (QM) model chemistries. Parametrization involved reoptimizing available parameters as well as extending the force field to new molecules with the goal of achieving self-consistency with respect to the Lennard-Jones and electrostatic parameters targeting QM and experimental hydration free energies. The resulting force field parameters achieve consistent treatment across the studied anions, facilitating more balanced simulations of biomolecules and small organic molecules in the context of the classical Drude polarizable force field. [ABSTRACT FROM AUTHOR]

We produced aniline cations (c –C 6 H 5 NH 2 +) and their dehydro- (H-loss) cations inside helium droplets by electron ionization and observed their mass-selected vibrational spectra in the N H stretching region. We observed vibrational bands at m/q = 93 which were identified as aniline cations. These bands showed only a few cm−1 shifts from the symmetric and anti-symmetric N H stretching bands for the amino (NH 2) group in the gas phase. For the H-loss cation at mass m/q = 92, the agreement of the observed N H band frequency with the result of DFT calculations suggests several candidate species, including a seven-membered ring structure, 4-monodehydro azepinylium (c –C 6 NH 6 +). A new reaction pathway to this cation was discussed by considering large excess energy in the ionization process. [Display omitted] • Aniline cations were produced in cold helium nanodroplets by electron ionization. • Both symmetric and anti-symmetric N–H stretching vibrational bands were observed. • H-loss fragment cations were found at m/q = 92 with a new N–H vibrational peak. • DFT calculations suggest candidate structures at 92 including a seven-membered ring. [ABSTRACT FROM AUTHOR]

For more than two decades, encapsulation in superfluid helium nanodroplets has served as a reliable technique for probing the structure and dynamics of molecules and clusters at a low temperature of ≈0.37 K. Due to weak interactions between molecules and the host liquid helium, good spectral resolution can usually be achieved, making helium droplets an ideal matrix for spectroscopy in a wide spectral range from infrared to ultraviolet. Furthermore, rotational structure in the spectra of small molecules provides a unique probe for interactions with the superfluid on an atomic scale. This review presents a summary of results and a discussion of recent experimental developments in helium droplet spectroscopy with the emphasis laid on infrared studies. Initially, studies focused on single molecules and have been expanded to larger species, such as metal-molecular clusters, biomolecules, free radicals, ions, and proteins.

Molecular ions in the magnetosphere can be a tracer of fast ion outflows from the deep ionosphere. Statistical properties of molecular ions (O2+/NO+/N2+) in the ring current are investigated based on ion composition measurements (<180 keV/q) by medium‐energy particle experiments‐electron analyzer and low‐energy particle experiments‐ion mass analyzer instruments on board the Arase (Exploration of energization and Radiation in Geospace, ERG) satellite. The investigated period from late March to December 2017 includes 11 geomagnetic storms with the minimum Dst index less than −40 nT. The molecular ions are observed in the region of L = 2.5–6.6 and clearly identified at energies above ~12 keV during most magnetic storms. During quiet times, molecular ions are not observed. The average energy density ratio of the molecular ions to O+ is ~3%. The ratio tends to increase with the size of magnetic storms. Existence of molecular ions even during small magnetic storms suggests that the fast ion outflow from the deep ionosphere occurs frequently during geomagnetically active periods. Plain Language Summary: Molecular ions usually exist only in the low‐altitude (< 300 km) deep ionosphere and cannot escape to space without a fast ion outflow to overcome a rapid loss due to dissociative recombination. Thus, molecular ion escape from the terrestrial atmosphere to space can be used as a tracer of effective ion loss from the deep ionosphere. Here we report new observations by Arase satellite that enables definitive identification of molecular ions by frequent time‐of‐flight mode observations. The statistical analysis shows that molecular ions exist in near‐Earth space during most magnetic storms, while they are not detected during geomagnetically quiet periods. The existence of molecular ions even during small magnetic storms suggests that the magnetic storm is an effective driver of the ion loss from the deep terrestrial ionosphere. Key Points: Frequent TOF‐mode ion composition measurements by Arase revealed statistical properties of molecular ions in the ring currentThe molecular (O2+/NO+/N2+) ions are commonly observed during geomagnetically active periods even during small magnetic stormsThe results suggest that the rapid ion outflow from the deep ionosphere occurs frequently during active periods [ABSTRACT FROM AUTHOR]

Experiments with cold ion–atom mixtures have recently opened the way for the production and application of ultracold molecular ions. Here, in a comparative study, we theoretically investigate ground and several excited electronic states and prospects for the formation of molecular ions composed of a calcium ion and an alkali-metal atom: CaAlk ^+ (Alk = Li, Na, K, Rb, Cs). We use a quantum chemistry approach based on non-empirical pseudopotentials, operatorial core-valence correlation, large Gaussian basis sets, and full configuration interaction method for valence electrons. Adiabatic potential energy curves, spectroscopic constants, and transition and permanent electric dipole moments are determined and analyzed for the ground and excited electronic states. We examine the prospects for ion-neutral reactive processes and the production of molecular ions via spontaneous radiative association and laser-induced photoassociation. After that, spontaneous and stimulated blackbody radiation transition rates are calculated and used to obtain radiative lifetimes of vibrational states of the ground and first-excited electronic states. The present results pave the way for the formation and spectroscopy of calcium–alkali-metal-atom molecular ions in modern experiments with cold ion–atom mixtures.