Molecular Ions Research Articles

Freezing Conformers for Gas-Phase Förster Resonance Energy Transfer.

Various techniques are available to illuminate geometric structures of molecular ions in gas phase, such as Förster Resonance Energy Transfer (FRET) informing on distances between two dyes covalently attached to a molecule. Typically, cationic rhodamines, which absorb and emit visible light, are used for labeling. Extensive work has revealed that the transition energy of a rhodamine is intricately linked to its nearby microenvironment, with nearby charges causing Stark-shifted emission. This occurs because the inter-dye Coulomb interaction is weaker in the excited state (S1) than in the ground state (S0) due to the increase in polarizability upon excitation. Therefore, absorption and emission spectra, along with FRET efficiencies, provide insights into structural motifs. At room temperature, multiple conformers often co-exist, leading to overlapping absorption bands among different conformers and broad spectra. To study specific conformers, it is necessary to isolate them, for example, using ion-mobility spectrometry. Another approach is to reduce temperature, which results in spectral narrowing and distinct absorption bands, allowing for the selection of specific conformers through selective excitation. Here, we describe the instrumentation used for cryogenically cold FRET experiments and discuss recent results for small model systems, as well as future directions for a technique still in its infancy.

The Selectively Nontargeted Analysis of Halogenated Disinfection Byproducts in Tap Water by Micro-LC QTOFMS.

With the rapid development of society, more and more unknown halogenated disinfection byproducts (DBPs) enter into drinking water and pose potential risks to humans. To explore the unknown halogenated DBPs in tap water, a selectively nontargeted analysis (SNTA) method was developed by conducting micro-liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (micro-LC-QTOFMS). In this method, two runs were employed: in the first run, the modes of TOFMS and precursor ion (the fragments were set as Cl35/Cl37, Br79/Br81, and I126.9) were performed, and the molecular ions or precursor ions of the halogenated organics could be obtained; in the second run, the product ion mode was conducted by setting the molecular ion screened above, and the MS/MS spectrums could be acquired to speculate concerning the structure. Two kinds of model DBPs (one kind had an aliphatic structure and the other was an aromatic compound) were used to optimize the parameters of the MS, and their MS characteristics were summarized. With this SNTA method, 15 halogenated DBPs were screened in two tap water samples and their structures were proposed. Of them, six DBPs had not been reported before and were assumed to be new DBPs. Overall, the detected halogenated DBPs were mostly acidic substances.

High performance PVC/ [AMI]mNTF2 ionic gel sensors for smart wearable applications

Plasticized polyvinyl chloride (PVC) gel as an electroactive polymer material has attracted increasing interest for the construction of flexible devices with the integration of actuation and self-sensing. However, the insufficient sensing ability of traditional PVC gels limits their applications. In this paper, a PVC ionic gel sensor based on the physical blending of PVC gel and the ionic liquid 1-allyl-3-methylimidazolium bisimide ([AMI]mNTF2) is presented. With the addition of ionic liquids, the PVC molecular chains and ions formed stable conductive pathways, resulting in increased conductivity and sensing performance of the PVC gel. The proposed sensor exhibits excellent sensing properties of high resolution (0.12 %) and fast response time (95 ms), along with high sensitivity (GF=27.8), which is more than seven times that of the traditional PVC gel. Furthermore, it was successfully utilized for human motion detection and remote control of a robotic hand, demonstrating the feasibility of the sensor for smart wearable applications in the future.

Deciphering the role of three-color synthesized laser pulse parameters in N2 ionization and attosecond pulse shaping

Photoionization of atoms or molecules is a fundamental process in strong-field physics, essential for generating high-order harmonics and producing attosecond pulses. Here, we investigate how a three-color laser field, consisting of wavelengths at 800 nm and its second and third harmonics, photoionizes N2 molecules and evaluates its effect on the properties of attosecond pulses. It has been discovered that by altering the relative phase, these harmonics periodically influence molecular ionization, increasing the discreteness and strength of the attosecond pulse trains. Three-color field driving dramatically raises the pulse peak while decreasing the width of the strongest peak pulse, whereas two-color field driving just slightly enhances the pulse intensity and duration. Furthermore, the effectiveness of harmonic production is significantly increased by varying the laser intensity ratios. Even though the efficiency and pulse intensity of the three-color field are limited by conversion efficiency, attosecond pulses with higher intensities can be produced with proper parameter tuning at lower ionization rates. These findings offer a significant foundation for precisely controlling attosecond pulse generation. Ocis codes320.7110; 320.7120.

Cross Sections for Electron Collisions with the CO2 Molecule and CO2+ Molecular Ion

Electron collision cross section data are complied from the literature for electron collisions with the carbon dioxide molecule, CO2 and the CO2+ ion. Cross sections are collected and reviewed for total scattering, elastic scattering, momentum transfer, rotational excitation, vibrational excitation, electronic excitation, dissociative processes and ionization. The literature has been surveyed up to the end 2023. For each of these processes, the recommended values of the cross sections are presented with an estimated uncertainty.

Is There an Adduct of Pyridine N-Oxide and Boron Trifluoride in the Gaseous State? Gas Electron Diffraction vs Mass Spectrometry.

A study of saturated vapor over the pyridine N-oxide-boron trifluoride (PyO-BF3) adduct was carried out at T = 448(5) K by a synchronous gas electron diffraction/mass spectrometry (GED/MS) experiment. Due to the absence of ions in the mass spectrum, indicating the presence of a structure with an O-B dative bond, several models of vapor composition were tested by the GED method. It was found that the dominant molecular form (up to 100%) in vapor is the PyO-BF3 adduct. Using the DFT/M06-2X/aug-cc-pVTZ method, geometric optimization of the molecular ion [PyO-BF3]+ was carried out, which showed its intrinsic instability and dissociation into a [PyO]+ cation and a BF3 molecule. This study certainly demonstrates the significant advantage of the GED method to determine the qualitative and quantitative gas-phase composition of dative-bonded adducts and other noncovalent complexes as well, whereas the interpretation of mass spectra may be ambiguous due to the possible intrinsic instability of ions containing a dative bond. The nature of the O-B bond is discussed in terms of the natural bond orbitals (NBOs) and the quantum theory of atoms in molecules (QTAIM). A comparison of structural and energetic parameters for PyO-BF3 and the previously studied BF3 adducts allows the theoretical comprehension of the nature of the O-B bond to be extended and to explain the different thermal stabilities of these compounds.

Electron Binding Energies of Open-Shell Species from Diagonal Electron-Propagator Self-Energies with Unrestricted Hartree-Fock Spin-Orbitals.

For closed-shell molecules, valence electron binding energies may be calculated accurately and efficiently with ab initio electron-propagator methods that have surpassed their predecessors. Advantageous combinations of accuracy and efficiency range from cubically scaling methods with mean errors of 0.2 eV to quintically scaling methods with mean errors of 0.1 eV or less. The diagonal self-energy approximation in the canonical Hartree-Fock basis is responsible for the enhanced efficiency of several methods. This work examines the predictive capabilities of diagonal self-energy approximations when they are generalized to the canonical spin-orbital basis of unrestricted Hartree-Fock (UHF) theory. Experimental data on atomic electron binding energies and high-level, correlated calculations in a fixed basis for a set of open-shell molecules constitute standards of comparison. A review of the underlying theory and analysis of numerical errors lead to several recommendations for the calculation of electron binding energies: (1) In calculations that employ the diagonal self-energy approximation, Koopmans's identity for UHF must be qualitatively correct. (2) Closed-shell reference states are preferable to open-shell reference states in calculations of molecular ionization energies and electron affinities. (3) For molecular electron binding energies between doublets and triplets, calculations of electron detachment energies are more accurate and efficient than calculations of electron attachment energies. When these recommendations are followed, mean absolute errors increase by approximately 0.05 eV with respect to their counterparts obtained with closed-shell reference orbitals.

Resonance electron capture by perylene molecules. Relation with negative differential conductance

Five resonant states of long-lived negative molecular ions were defined during the gas-phase resonant electron capture by perylene. Three states are the ground state (0.05 eV) and two shape resonances (0.4 eV and 0.7 eV). Core-excited Feshbach resonance (1.4 eV) transits into a quartet state, which delays the autodetachment of additional electron and causes the negative differential conductance in tunneling transition due to the spin prohibition. Inter-shell resonance (2.5 eV) is mixed with the ground state with the same symmetry and is likely to be stabilized through the light emission with simultaneous transition to a quartet state.

Efficient Control of Electron Localization and Probability Modulation with Synthesized Two-Color Intense Laser Pulses.

A coupled electron-nuclear dynamical study at attosecond time scale is performed on the HD+ and H2+ molecular ions under the influence of synthesized intense two-color electric fields. We have employed ω - 2ω and also, ω - 3ω two-color fields in the infrared/mid-infrared regime to study the different fragmentation processes originating from the interference of n - (n + i) (i = 1, 2) photon absorption pathways. The branching ratios corresponding to different photofragments are controlled by tuning the relative phase as well as intensity of the two-color pulses, while the effect of the initial nuclear wave function is also studied by taking an individual vibrational eigenstate or a coherent superposition of several eigenstates of HD+ and H2+. By comprehensive analysis, the efficacy of the two different types of synthesized two-color pulses (ω - 2ω and ω - 3ω) are analyzed with respect to one-color intense pulses in terms of controlling the probability modulation and electron localization asymmetry and compared with previous theoretical calculations and experimental findings. Through the detailed investigation, we have addressed which one is the major controlling knob to have better electron localization as well as probability modulation.

On the Synthesis, Characterization and Applications of Para-nitro Aniline-based Reactive Dye

The dye was synthesized by nitration of aniline to para-nitro aniline, diazotization and coupling reactions. The melting point of the para-nitro aniline was taken to yield 147ºC. The result from the GC-MS shows that the compound with the highest relative abundance of 100% showed a molecular ion peak of 129.4 compounds which correspond to lower relative abundance. Also from the GC-MS result, the two peaks of masses 57.5 g and 83.4 g respectively correspond to fragments of the samples. Ultra-violet spectrophotometer was used to determine the absorption of the dye. The para-nitro aniline dye as synthesized showed the highest absorbance of 2.214 at 220 nanometers. The dye was applied to pure cotton and cellulose. The percentage shift of the dye toward the fabric i.e. percentage exhaustion of the dye was calculated to yield 73% which shows that the reactive dye has high exhaustion value. Fastness test was carried out on the dyed fabric to characterize the material’s color resistance to fading and running. These tests are heat, light and wash fastness which is rated 1-5 according to Ukponwam and Odilora (2000) where 1 shows poor fastness and 5 very good fastness. The wash, heat and light fastness of 4, 5 and 5 respectively shows that the dyed fabric has an excellent fastness to washing, heating and sun drying.

Qualitative analysis of licorice and strychnine decoction before and after combination using UPLC-QE-Orbitrap-MS.

Glycyrrhiza glabra L. (GG) and Strychnos nux-vomica L. (NV) are traditional Chinese medicines (TCMs). Changes in the chemical composition may occur before and after the GG-NV compatibility. Ultra-performance liquid chromatography Q-exactive Orbitrap mass spectrometry (UPLC-QE-Orbitrap-MS) was applied here to study the difference in the components of the GG and NV decoctions before and after they were combined. The changes in the chemical composition of GG and NV before and after the combination were determined. The precise molecular weight, retention time, and fragment ion peak of the different components of the decoctions before and after compatibility were obtained through UPLC-QE-Orbitrap-MS. Differential analysis methods, such as principal component analysis, were used for comparison. In the positive ion mode, 200 new components were added, whereas six components were lost. In the negative ion mode, 144 new compounds were identified, whereas three components were missing. The compatibility difference between GG and NV was studied through UPLC-QE-Orbitrap-MS. The chemical composition of GG and NV changed before and after compatibility, and a class of compounds different from GG and NV was identified in the co-decoction. This study provides an experimental basis for subsequent research into detoxification mechanisms of the GG-NV combination and offers a new analytical method for investigating the compatibility of various other TCM pairs.

Quantum state tracking and control of a single molecular ion in a thermal environment.

Understanding molecular state evolution is central to many disciplines, including molecular dynamics, precision measurement, and molecule-based quantum technology. Details of the evolution are obscured when observing a statistical ensemble of molecules. Here, we report real-time observations of thermal radiation-driven transitions between individual states ("jumps") of a single molecule. We reversed these "jumps" through microwave-driven transitions, resulting in a twentyfold improvement in the time the molecule dwells in a chosen state. The measured transition rates showed anisotropy in the thermal environment, pointing to the possibility of using single molecules as in-situ probes for the strengths of ambient fields. Our approaches for state detection and manipulation could apply to a wide range of species, facilitating their uses in fields including quantum science, molecular physics, and ion-neutral chemistry.

A low cosmic-ray ionisation rate in the pre-stellar core Ophiuchus/H-MM1

A low cosmic-ray ionisation rate in the pre-stellar core Ophiuchus/H-MM1

In situ measurement of electron emission yield at Si and SiO2 surfaces exposed to Ar/CF4 plasmas

Abstract Plasma simulations require accurate yield data to predict the electron flux that is emitted when plasma-exposed surfaces are bombarded by energetic particles. One can measure yields directly using particle beams, but it is impractical to create a separate beam of each particle produced by typical plasmas. In contrast, measurements made in situ, during plasma exposure, provide useful values for the total emitted flux and effective yield produced by all incident particles. Here, in situ measurements were made at thermally oxidized and bare silicon wafers placed on the radio-frequency (rf) biased electrode of an inductively coupled plasma system. The rf current and voltage across the sheath at the wafer were measured, along with Langmuir probe measurements of ion current density and electron temperature. The measurements are input into a numerical sheath model, which allows the emitted electron current to be distinguished from other currents. The effective yield, i.e. the ratio of the total emitted electron flux to the incident ion flux, was determined at incident ion energies from 40 eV to 1.4 keV, for Si and SiO2 surfaces in Ar, CF4, and Ar/CF4 mixtures at 1.33 Pa (10 mTorr). Yields for Ar plasmas are compared with previous work. For SiO2 surfaces in Ar/CF4 mixtures and pure CF4, the yield is dominated by ion kinetic emission, which is the same for all mixtures, and, presumably, for all ions. For Si surfaces in Ar/CF4 and CF4, the yield at high energies can be explained in part by fragmentation of molecular ions, and the yield from Ar+ can be distinguished from the other ionic species. Analytic fits of the yields are provided for use in plasma simulations.

Attosecond delays in X-ray molecular ionization.

The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics1-7. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization8-12. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700 as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger-Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.

Prediction of titanium burn-off and untimate titanium content in electroslag process

In this study, we investigate the burning behavior of titanium during the electroslag remelting (ESR) process and its impact on the titanium content at the endpoint using machine learning. Initially, a comprehensive database was established by collecting data from literature and experiments, encompassing slag system composition, smelting temperature, and material composition content. Subsequently, six machine learning algorithms, including random forest and Bayesian regression, were employed to model the burning loss behavior of titanium. The random forest model, which exhibited optimal mean square error (MSE) performance, was utilized to generate partial dependence plots. These plots, in conjunction with experimental observations and existing studies, facilitated the analysis of key factors influencing titanium burn loss. Furthermore, the same six machine learning models were applied to predict the endpoint titanium content. The Bayesian regression model demonstrated superior performance in terms of R2 and MSE, leading to the derivation of an empirical formula for predicting endpoint titanium content. This empirical formula was subsequently validated, refined, and optimized using a thermodynamic model based on the theory of molecular ion coexistence. The final prediction formula achieved an error margin of 0.123%.

Organometallic Ionic Plastic Crystals Incorporating Cationic Half-Sandwich Complexes.

Ionic plastic crystals (IPCs), characterized by nearly spherical molecular ions, exhibit remarkable solid-state characteristics including high ionic conductivity. However, most IPCs are organic onium salts. Incorporating organometallic half-sandwich complexes into IPCs is challenging owing to their low-symmetry structures. This paper introduces a novel series of IPCs composed of salts derived from half-sandwich organometallic complexes. We synthesized five salts of [Ru(Cp)(tmeda)(CO)]X (tmeda = N,N,N',N'-tetramethyl-1,2-ethanediamine, X = anion) with different anions and examined their phase behavior, crystal structures, and molecular motion in the solid-state. Salts featuring the CPFSA (= 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonimide), B(CN)4-, and FSA- (= (FSO2)2N-) anions underwent phase transitions to an IPC phase with a CsCl-type structure in the temperature range of 327-364 K. Employing smaller anions led to an increase in the transition temperature. In each salt, the coordination number, representing the number of anions surrounding one cation, remained eight in IPC and low-temperature phases. However, salts containing smaller anions (CF3BF3- and PF6-) displayed a rotator phase rather than the IPC phase. In these cases, the coordination numbers were six at low temperatures.

Cool Classical EI - A New Standard in EI and Its Many Benefits.

GC-MS with Cold EI improves all of the central GC-MS performance aspects, but it is known mostly for its provision of enhanced molecular ions. This occasionally leads to the misconception that, like chemical ionization, Cold EI is a supplementary ion source to standard EI. However, Cold EI is a highly superior replacement ion source to standard EI. While Cold EI mass spectra are the most informative and fully compatible with mass spectral library (such as NIST) identification, in some cases, the Cold EI mass spectra with their enhanced molecular ions result in a "picture" that is not as one is used to seeing. In this paper, we describe the "Cool Classical EI" mode, which produces classical EI mass spectra like standard EI. The change of Cold EI into the Cool Classical EI mode is software-based, requires no hardware change, and can be achieved even during the analysis. Several mass spectra that were obtained in the Cool Classical EI mode are presented and compared with standard EI and Cold EI mass spectra. In this paper we further demonstrate and discuss several benefits that Cold EI brings that are retained while using Cool Classical EI, including (a) much faster speed of analysis, (b) uniform response, (c) extended range of compounds amenable for analysis, (d) improved sample identification, (e) elimination of ion source related peak tailing, (f) elimination of intraion-source degradation, and (g) better signal-to-noise ratio of the sample compounds.

Low-energy atomic and molecular hydrogen ion interaction with low-work function electride 12CaO · 7Al2O3

To efficiently generate H− ions from positive atomic or molecular hydrogen beams injected onto a solid surface, it has been suggested to use a material with a low-work function as the target material. However, it is not clear under what conditions the most efficient H− production is realized for incident beam parameters or reflection angles. Therefore, we studied the interaction between low-energy atomic and molecular hydrogen beams (less than 1 keV/nucleon) with a low-work function electride 12CaO⋅7Al2O3 (C12A7). The production ratio of H− to H+ ions from the C12A7 electride was much higher than Mo targets with higher work functions, especially at smaller incident and smaller reflection angles. The H− to H+ production ratio slightly increased as the incident energies were decreased, but there was no significant difference between the electride and Mo targets. These results indicate that smaller incident angles and lower beam energies of the incident hydrogen beam are favorable for the enhancement of the production ratio of H− to H+ ions in C12A7. The higher production ratio appeared at the vertical beam energies less than on the order of 100 eV, where quantum mechanical processes may become important.

Photodissociation spectra of single trapped CaOH+ molecular ions.

Molecular ions that are generated by chemical reactions with trapped atomic ions can serve as an accessible testbed for developing molecular quantum technologies. On the other hand, they are also a hindrance to scaling up quantum computers based on atomic ions, as unavoidable reactions with background gases destroy the information carriers. Here, we investigate the single- and two-photon dissociation processes of single CaOH+ molecular ions co-trapped in Ca+ ion crystals using a femtosecond laser system. We report the photodissociation cross section spectra of CaOH+ for single-photon processes at λ = 245-275 nm and for two-photon processes at λ = 500-540 nm. Measurements are interpreted with quantum-chemical calculations, which predict the photodissociation threshold for CaOH+ → Ca+ + OH at 265nm. This result can serve as a basis for dissociation-based spectroscopy for studying the internal structure of CaOH+. The result also gives a prescription for recycling Ca+ ions in large-scale trapped Ca+ quantum experiments from undesired CaOH+ ions formed in the presence of background water vapor.