Dissociative Ionization Research Articles

Theory-Enabled High-Throughput Screening of Ion Dissociation Explains Conductivity Enhancements in Diluted Ionic Liquid Mixtures

Theory-Enabled High-Throughput Screening of Ion Dissociation Explains Conductivity Enhancements in Diluted Ionic Liquid Mixtures

Ab initio study of electronic states and radiative properties of the AcF molecule.

Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35 000 cm-1 are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IPe = 48 866 cm-1, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the T,P-violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving a mean uncertainty estimate of ∼450 cm-1 for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck-Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable (1)3Δ1 state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1ms.

Beyond vanilla: The dissociation mechanism of vanillin in four charge states

We compare the unimolecular decay mechanism of vanillin in four charge states. The unimolecular thermal decomposition of the neutral and dissociative ionization reactions in the cation have already been addressed in synchrotron-based photoionization studies. The picture is completed here by studying the collision-induced dissociation mechanism of protonated vanillin cations and deprotonated vanillin anions in the 5–30 eV collision energy range. The mass spectrometric observations are rationalized by ab initio calculations, which reveal the mechanism and the energetics of dissociation pathways. In the positive ion mode, the aldehyde oxygen is protonated, after which CO is lost. In contrast to previous results, CO loss is found to be the sole primary fragmentation pathway of protonated vanillin. Two hydrogen migration steps to the benzene ring open sequential CH3OH and CH3 loss channels to yield C6H5O+ and C6H6O2+, respectively. The former fragment ion can continue to lose CO, associated with ring contraction and producing the cyclopentadiene cation, C5H5+. In the negative ion mode, the proton is removed from the hydroxyl group. The primary dissociation channel of deprotonated vanillin corresponds to (C)OCH3 bond breaking in the methoxy group to form C7H4O3− at m/z 136. This species goes on to produce C6H4O2− and C6H4O− anions via CO and CO2 loss, respectively, in sequential dissociation processes at higher collision energies. We compare the protonated and deprotonated vanillin fragmentation pathways with those observed in the decomposition of neutral vanillin and with the dissociation pathways of the vanillin cation. The initial decomposition step for neutral, cationic, and deprotonated vanillin is methyl loss by direct CO bond breaking, often followed by loss of CO. In contrast, protonated vanillin first loses CO after isomerization.

Solid polymer electrolytes based on a high dielectric polymer and ionic liquids for lithium batteries

Solid-state batteries were produced using new solid polymer electrolytes (SPEs) based on the high dielectric constant polymer poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene), P(VDF-TrFE-CFE) and 40 wt% of different ionic liquids (IL) sharing the same bis(trifluoromethylsulfonyl)imide [TFSI] anion and different cations. The morphological, thermal, mechanical and electrochemical properties of the SPEs were investigated, as a function of the interaction between IL and polymer matrix. The addition of IL increased the amorphous phase of the polymer with respect to the neat polymer, leading to room temperature ionic conductivity values between 2.3 × 10−5 and 1.4 × 10−4 S cm−1, depending on the specific IL. Further, the highest lithium transference number of 0.71 was obtained for the [PMPyrr][TFSI] sample. Li/LiFePO4 half batteries using these SPEs show excellent and stable battery performance at room temperature at different C-rates. The highest discharge capacity value is achieved for the [PMPyrr][TFSI] sample, reaching 137 mAh.g−1 and 117 mAh.g−1 at C/10 and C/2 rates, respectively, with high coulombic efficiency (∼100%) and low capacity fade after 100 cycles. The use of P(VDF-TrFE-CFE) allows the development of room temperature solid-state lithium-ion batteries and the improved results are associated to the high polymer dielectric constant which facilitates IL ions dissociation, improving SPE ionic mobility.

Dehydrogenation in Electron-Induced Dissociative Ionization of Pyridine Molecule

"The electron-impact dissociative ionization of pyridine has been investigated using mass spectrometry. Thirty-two well-resolved mass peaks have been identified in the cation mass spectra and assigned to the most likely ionic molecular fragments. The new sixteen ionic fragments' appearance energies have been determined, and sixteen others remeasured. The total cross-section for electron-impact ionization of pyridine has been measured at 100 eV. Thorough analysis indicates that at least three peaks' groups in the mass spectra occur via the shake-off dehydrogenation mechanism, i.e., by sequential hydrogen atoms elimination from the pyridine parent cation or its fragmentation products. The nature of this process is deciphered. "

Potential Energy Curves of the Low-Lying Five 1Σ+ and 1Π States of a CH+ Molecule Based on the Free Complement - Local Schrödinger Equation Theory and the Chemical Formula Theory.

The potential energy curves (PECs) of the low-lying five 1Σ+ and 1Π states (X1Σ+, C1Σ+, 31Σ+, A1Π, and D1Π states) of a CH+ molecule, an important interstellar molecule, were calculated by the free complement (FC) - local Schrödinger equation (LSE) theory with the direct local sampling scheme. The FC wave functions were constructed based on the chemical formula theory (CFT), whose local characters correspond to the covalent dissociations: C+(2P°(s2p))) + H(2S) of the X1Σ+ and A1Π states and the ionic dissociations: C(1D(s2p2)) + H+ of the C1Σ+ and D1Π states. All the calculated PECs were obtained with satisfying the chemical accuracy, i.e., error less than 1 kcal/mol, as absolute total energy of the Schrödinger equation without any energy shift. The spectroscopic data calculated from the PECs agreed well with both experimental and other accurate theoretical references. We also analyzed the wave functions using the inverse overlap weights proposed by Gallup et al. with the CFT configurations. For the X1Σ+ and A1Π states, the covalent C+(sp2) and C+(p3) configurations played important roles for bond formation. In the small internuclear distances of the C1Σ+, D1Π, and 31Σ+ states, the covalent character was also dominant as a result of the electron charge transfer from C to H+. Thus, the present FC-LSE results not only are accurate but also can provide chemical understanding according to the CFT.

Pentafluorobenzylpyridinium: new thermometer ion for characterizing the ions produced by collisional activation during tandem mass spectrometry.

In this study, pentafluorobenzylpyridinium (F5-BnPy+), which has the highest dissociation energy among the reported benzylpyridinium thermometer ion, is proposed to characterize the internal energy distributions of ions activated by higher energy collisional dissociation (HCD) and ion-trap collision-induced dissociation (CID) during tandem mass spectrometry. The dissociation threshold energies of F5-BnPy+ was determined using quantum chemistry calculations at the CCSD(T)/6-311++G(d,p)//M06-2X-D3/6-311++G(d,p) level of theory, and the appearance energies for ion dissociation in HCD and ion-trap CID were estimated using Rice-Ramsperger-Kassel-Marcus theory. The main differences between HCD and ion-trap CID are the collision energies used and the timescales of collisional activation. For both HCD and ion-trap CID, the average internal energy of the ions increased with increasing collision energy. In contrast, the average value for the internal energy of the ions activated by ion-trap CID was lower than that of ions activated by HCD, probably because of the smaller collisional energy and longer activation time of the ion-trap CID experiments. The reported method will aid in the determination of the optimum tandem mass spectrometry parameters for the analysis of small molecules such as metabolites.

Solution and Gas-Phase Stability of DNA Junctions from Temperature-Controlled Electrospray Ionization and Surface-Induced Dissociation.

DNA three-way junction (TWJ) structures transiently form during key cellular processes such as transcription, replication, and DNA repair. Despite their significance, the thermodynamics of TWJs, including the influence of strand length, base pair composition, and ligand binding on TWJ stability and dissociation mechanisms, are poorly understood. To address these questions, we interfaced temperature-controlled nanoelectrospray ionization mass spectrometry (TC-nESI-MS) with a cyclic ion mobility spectrometry (cIMS) instrument that was also equipped with a surface-induced dissociation (SID) stage. This novel combination allowed us to investigate the structural intermediates of three TWJ complexes and examine the effects of GC base pairs on their dissociation pathways. We found that two TWJ-specific ligands, 2,7-tris-naphthalene (2,7-TrisNP) and tris-phenoxybenzene (TrisPOB), lead to TWJ stabilization, revealed by an increase in the melting temperature (Tm) by 13 or 26 °C, respectively. To gain insights into conformational changes in the gas phase, we employed cIMS and SID to analyze TWJs and their complexes with ligands. Analysis of IM arrival distributions suggested a single-step dissociation of TWJs and their intermediates for the three studied TWJ complexes. Upon ligand binding, a higher SID energy by 3 V (2,7-TrisNP) and 5 V (TrisPOB) was required to induce 50% dissociation of TWJ, compared to 38 V in the absence of ligands. Our results demonstrate the power of utilizing TC-nESI-MS in combination with cIMS and SID for thermodynamic characterization of TWJ complexes and investigation of ligand binding. These techniques are essential for the TWJ design and development as drug targets, aptamers, and structural units for functional biomaterials.

Extending Operation Temperature of Hydrogel for Zn Ion Batteries

Aqueous zinc ion batteries (ZIBs) provide one of the most promising technologies for large-scale electrochemical energy storage because they are environmentally friendly, safe, and have a low-cost. However, there are still some major challenges for the commercialization for ZIBs, such as Zn dendrite on Zn anode surface and poor low-temperature operation. The major problem related to the operation at low temperatures is that the water freezes below 0 C as a result of the bonding between the water molecules, especially the H-bond in the aqueous electrolyte. Modifying the solvation structure by using additives and concentrated electrolytes is among the most efficient ways to widen the operation temperature range of the aqueous electrolyte. In this presentation, we developed a hydrogel made from a commercial material, para-aramid fiber, combined with polyvinyl alcohol showing excellent anti-freezing performance even at -40 C. Due to the abundant and uniformly distributed hydrophilic oxhydryl on the polymer chain, the hydrogel is able to facilitate ion absorption and dissociation to promote the ion transport. The competition between water molecules and hydrophilic oxhydryl can improve the anti-freezing performance of the hydrogel. Our hydrogel demonstrates superior mechanical properties and high ionic conductivity down to -40 C, which opens the horizons for operating these batteries in large-scale energy storage at high latitudes. In addition, the developed hydrogel shows good protection to the Zn anode by preventing Zn dendrite growth and prolonged the lifetime of the Zn symmetric cell at both room and below-room temperatures.

Quantum simulation of non-Born–Oppenheimer dynamics in molecular systems by path integrals

A numerical algorithm based on the probabilistic path integral approach for solving Schrödinger equation has been devised to treat molecular systems without Born–Oppenheimer approximation in the nonrelativistic limit at zero temperature as an alternative to conventional variational and perturbation methods. Using high-quality variational trial functions and path integral method based on generalized Feynman–Kac method, we have been able to calculate the non-Born–Oppenheimer energy for hydrogen molecule for the [Formula: see text] state and hydrogen molecular ion. Combining these values and the value for ionization potential for atomic hydrogen, the dissociation energy and ionization potential for hydrogen molecules have been determined to be 36 113.672(3)[Formula: see text]cm[Formula: see text] and 124 446.066(10)[Formula: see text]cm[Formula: see text], respectively. Our results favorably compare with other theoretical and experimental results and thus show the promise of being a nonperturbative alternative for testing fundamental physical theories.

Linear, nonlinear rheological properties and foamability of Surlyn partially neutralized with sodium counterion

Linear viscoelasticity (LVE), elongational rheological behavior, and foamability are examined for ionomer samples based on a commercial Surlyn sample: The Surlyn sample is dialyzed back into the parent acid copolymer and partially neutralized by sodium hydroxide to different degrees. The LVE pseudo-master curves shift to the lower frequency with an increase in the molar fraction of sodium, reflecting the increased activation energy for ionic dissociation. Incorporation of this energy into the sticky-double-reptation model gives good prediction of the LVE behavior. The degree of strain hardening under the extensional flow exhibits a non-monotonous change: the transient hardening first intensifies with increasing the ion content up to ∼50 mol%, and then weakens upon further increasing the ion content. The foamability of these samples in supercritical CO2 appears to be controlled by the flowability as well as the melt strength during the elongational flow. In particular, the foaming T window widens greatly when the strain-hardening has been strengthened by the physical network based on the ionic interaction.

Acetylacetone Photolysis at 280 nm Studied by Velocity-Map Ion Imaging.

The photolysis of acetylacetone (AcAc) has been studied using velocity-map ion imaging with pulsed nanosecond lasers. The enolone tautomer of AcAc (CH3C(O)CH═C(OH)CH3) was excited in the strong UV absorption band by UV pulses at 280 nm, preparing the S2(ππ*) state, and products were probed after a short time delay by single-photon VUV ionization at 118.2 nm. Two-color UV + VUV time-of-flight mass spectra show enhancement of fragments at m/z = 15, 42, 43, 58, and 85 at the lowest UV pulse energies and depletion of the parent ion at m/z = 100. Ion images of the five major fragments are all isotropic, indicating dissociation lifetimes that are long on the timescale of molecular rotation but shorter than the laser pulse duration (<6 ns). The m/z = 15 and 85 fragments have identical momentum distributions with moderate translational energy release, suggesting that they are formed as a neutral product pair and likely via a Norrish type I dissociation of the enolone to form CH3 + C(O)CH═C(OH)CH3 over a barrier on a triplet surface. The m/z = 43 fragment may be tentatively assigned to the alternative Norrish type I pathway that produces CH3CO + CH2C(O)CH3 on S0 following phototautomerization to the diketone, although alternative mechanisms involving dissociative ionization of a larger primary photoproduct cannot be conclusively ruled out. The m/z = 42 and 58 fragments are not momentum-matched and consequently are not formed as a neutral pair via a unimolecular dissociation pathway on S0. They also likely originate from the dissociative ionization of primary photofragments. RRKM calculations suggest that unimolecular dissociation pathways that lead to molecular products on S0 are generally slow, implying an upper-limit lifetime of <46 ns after excitation at 280 nm. Time-dependent measurements suggest that the observed photofragments likely do not arise from dissociative ionization of energized AcAc S0*.

Review of fragmentation of synthetic single-stranded oligonucleotides by tandem mass spectrometry from 2014 to 2022.

The fragmentation of oligonucleotides by mass spectrometry allows for the determination of their sequences. It is necessary to understand how oligonucleotides dissociate in the gas phase, which allows interpretation of data to obtain sequence information. Since 2014, a range of fragmentation mechanisms, including a novel internal rearrangement, have been proposed using different ion dissociation techniques. The recent publications have focused on the fragmentation of modified oligonucleotides such as locked nucleic acids, modified nucleobases (methylated, spacer, nebularine and aminopurine) and modification to the carbon 2'-position on the sugar ring; these modified oligonucleotides are of great interest as therapeutics. Comparisons of different dissociation techniques have been reported, including novel approaches such as plasma electron detachment dissociation and radical transfer dissociation. This review covers the period 2014-2022 and details the new knowledge gained with respect to oligonucleotide dissociation using tandem mass spectrometry (without priori sample digestion) during that time, with a specific focus on synthetic single-stranded oligonucleotides.

Analysis for disulfide bonds in polypeptide sequences based on ultraviolet photodissociation combined with linear ion trap mass spectrometry

The analysis of dissociation products of disulfide bonds in peptide sequences has been increasingly applied in various fields. Ion dissociation is typically performed by tandem mass spectrometry, in which the overall molecular weight is determined during the first stage and the protein sequence and structure are obtained by dissociation during the second stage. However, conventional dissociation methods have some disadvantages, such as insufficient dissociation efficiency, and low product signals and varieties. Ultraviolet photodissociation (UVPD) is a rapid, efficient, and practical dissociation method for protein analysis, which excites the biomolecule skeleton and then directly excites the molecules, forming the excited states within microseconds. Although the development of mass spectrometer platforms coupled with UVPD has been reported to date, most of these studies have focused on the application of UVPD in mass spectrometry (MS). Discussions on the experimental setup for UVPD lasers, including the trigger process of the ultraviolet (UV) laser, the timing sequence of the entire dissociation and detection process, and their influence on dissociation, are limited. Therefore, an instrument platform was developed with a linear ion-trap mass spectrometer and an excimer laser to achieve UVPD by adjusting the laser trigger signal. The platform dissociated the disulfide bond of the amino acid sequence ARACAKA-ECG into two characteristic valence states (m/z = 498 and 332), and their highest intensities were obtained by optimizing the experimental conditions of the platform. The dissociation results of UVPD showed the characteristic peaks of ARACAKA (m/z 345) that were produced by disulfide bond cleavage, but these peaks were not detected by collision-induced dissociation (CID). Therefore, it was confirmed that the developed platform realized UVPD of the disulfide bond of the amino acid sequence of the polypeptide. Moreover, the developed platform provides a reference for the implementation of UVPD for peptide sequencing.

Dissociative electron attachment to 1- and 9-chloroanthracene in the gas phase

Dissociative electron attachment (DEA) to 1-chloroanthracene and 9-chloroanthracene was investigated under gas-phase conditions. In both compounds, the elimination of the chlorine anion is the dominant channel for the dissociation of molecular negative ions (NIs). The second most intense channel leads to the formation of molecular anions (Mˉ). The autodetachment lifetime of Mˉ was measured to be about 170 μs for both compounds. The widths of the Mˉ peaks indicate that molecular anions are formed via two resonances: at thermal electron energies and through a shape resonance at the energy of ∼0.5 eV. Adiabatic electron affinities were estimated in the framework of the simple Arrhenius model to be 0.86 eV for both molecules, the values being close to the theoretical predictions by DFT method of 0.90 eV and 0.93 eV for 1-chloroanthracene and 9-chloroanthracene respectively. Metastable negative ions are observed in the DEA spectra of both molecules, which testifies that the elimination of chlorine anions from molecular NIs appears on a time scale of several microseconds.

Dissociative electron attachment and dissociative ionization of CF3AuCNC(CH3)3, a potential FEBID precursor for gold deposition

Dissociative electron attachment and dissociative ionization of CF3AuCNC(CH3)3, a potential FEBID precursor for gold deposition

Attosecond delays between dissociative and non-dissociative ionization of polyatomic molecules

The interplay between electronic and nuclear motions in molecules is a central concept in molecular science. To what extent it influences attosecond photoionization delays is an important, still unresolved question. Here, we apply attosecond electron-ion coincidence spectroscopy and advanced calculations that include both electronic and nuclear motions to study the photoionization dynamics of CH4 and CD4 molecules. These molecules are known to feature some of the fastest nuclear dynamics following photoionization. Remarkably, we find no measurable delay between the photoionization of CH4 and CD4, neither experimentally nor theoretically. However, we measure and calculate delays of up to 20 as between the dissociative and non-dissociative photoionization of the highest-occupied molecular orbitals of both molecules. Experiment and theory are in quantitative agreement. These results show that, in the absence of resonances, even the fastest nuclear motion does not substantially influence photoionization delays, but identify a previously unknown signature of nuclear motion in dissociative-ionization channels. These findings have important consequences for the design and interpretation of attosecond chronoscopy in molecules, clusters, and liquids.

Identifying photoelectron releasing order in strong-field dissociative ionization of H2.

Driven by intense laser fields, the outgoing photoelectrons in molecules possess a quiver motion, resulting in the rise of the effective ionization potential. The coupling of the field-dressed ionization potential with abundant molecular dynamics complicates the laser-molecule interactions. Here, we demonstrate an approach to resolve photoelectron releasing order in the dissociative and non-dissociative channels of multiphoton ionization driven by an orthogonally polarized two-color femtosecond laser pulse. The photoelectron kinetic energy releases and the regular nodes in the photoelectron angular distributions due to the participation of different continuum partial waves allow us to deduce the field-dressed ionization potential of various channels. It returns the ponderomotive energy experienced by the outgoing electron and reveals the corresponding photoionization instants within the laser pulse. Our results provide a route to explore the complex strong-field ionization dynamics of molecules using two-dimensional photoelectron momentum spectroscopy.

Enhanced heat transfer in a microchannel with pseudo-roughness induced by Onsager-Wien effect

A three-dimensional numerical analysis of flow and conjugate heat transfer in a microchannel in the presence of the electric-field-induced Onsager–Wien effect is performed. A novel design is proposed to induce a pseudo-roughness effect in the microchannel and thereby increasing the heat transfer. A series of thin plate electrode pairs are flushed along the bottom wall of the microchannel. The electric-field-enhanced dissociation of ions induces the Onsager–Wien effect, and generates small flow vortices near the bottom wall of the channel. These flow vortices with sharp local velocity gradients effectively disrupt the viscous and thermal boundary layers, and thus, introduce a pseudo-roughness effect. This disruption of the boundary layers improves the heat transfer between the channel wall and the working fluid. The thermal and hydraulic performances in the microchannel are quantified as a function of the flow Reynolds number Re and electric Reynolds number ReEL. In general, the performance factor PF is higher when the flow and electric Reynolds numbers are higher. However, the associated pressure drop penalty reduces the PFPF<1 in viscous-effect-dominated flows at Re=250. By contrast, the Onsager–Wien effect increases the PF to a maximum value of 1.26 in inertia-dominated flows at Re=1000 and ReEL=15. A significant heat transfer enhancement is realized, even at a low applied voltage of ∼1 kV. The results of this study indicate that the pseudo-roughness produced by the electric-field-induced Onsager–Wien effect can substantially enhance the heat transfer in a microchannel with a trivial amount of additional power consumption. Results presented in this study will serve as a benchmark to design microchannels with enhanced heat transfer by using active vortex generation based on Onsager-Wien effect.

Carbonation inhibitor by polyethylene glycol encapsulation of calcium hydroxide fine particles to improve antimicrobial and root canal penetration properties

The carbonation of calcium hydroxide (Ca(OH)2) is affected by humidity and a saturated atmosphere. Ca(OH)2 from nature is easily carbonation and self-aggregates into calcium carbonate (CaCO3), resulting in larger particle size impairing the antimicrobial properties due to lack of penetration into the dentinal tubules and lower ion dissociation. To reduce the particle size, the wet beads milling process with distilled water as the medium is commonly used, but often results in great carbonation of the final product. Polyethylene Glycol (PEG) may inhibit the carbonation process as well as re-agglomeration. However, it requires intensive drying of the fine Ca(OH)2 particles. As an alternative, we used ethanol as a medium in the milling process, which is easily dried and compatible with PEG as a surfactant. This study aimed to evaluate PEG 400 as a dispersing agent in ethanol medium in the beads milling process to prevent carbonation of the fine Ca(OH)2 particles. The following groups were analysed CaP-PEG (Ca(OH)2-PEG) with ethanol as a medium, CaP-Eth (Ca(OH)2 with ethanol as a medium), CaP-DW (Ca(OH)2 with distilled water as a medium), CaPC (Ca(OH)2-carbonated) as the negative control and CaC (Ca(OH)2 analytical grade) as the positive control The final particle results were characterized to evaluate the crystal structure, functional groups, and particle size. The corresponding pH and antimicrobial activity against Enterococcus faecalis were assessed at 1, 3, 7, and 14 days. The penetration ability was evaluated by Scanning Electron Microscope. The data obtained were analysed by ANOVA with a significance level of 5%. PEG was able to inhibit carbonation and stabilize pH for up to 14 days, providing increased antimicrobial activity against E. faecalis. PEG also facilitates the ability of fine Ca(OH)2 particles to penetrate deeper into the dentine tubules by reducing particle size.