Ionization Of Water Molecules Research Articles

Water molecule ionization by proton impact experiment and GTO-First Born theory

SynopsisIn this communication we present calculations and measurements of water ionization by protons at intermediate and high impact energies. The main goal of the present theoretical approach is the development of a method to routinely incorporate sophisticated wavefunctions for small and medium-sized molecules in the determination of ionization cross-sections.

Length and Energy Dependence of Low-Energy Electron-Induced Strand Breaks in Poly(A) DNA.

The DNA in living cells can be effectively damaged by high-energy radiation, which can lead to cell death. Through the ionization of water molecules, highly reactive secondary species such as low-energy electrons (LEEs) with the most probable energy around 10 eV are generated, which are able to induce DNA strand breaks via dissociative electron attachment. Absolute DNA strand break cross sections of specific DNA sequences can be efficiently determined using DNA origami nanostructures as platforms exposing the target sequences towards LEEs. In this paper, we systematically study the effect of the oligonucleotide length on the strand break cross section at various irradiation energies. The present work focuses on poly-adenine sequences (d(A4), d(A8), d(A12), d(A16), and d(A20)) irradiated with 5.0, 7.0, 8.4, and 10 eV electrons. Independent of the DNA length, the strand break cross section shows a maximum around 7.0 eV electron energy for all investigated oligonucleotides confirming that strand breakage occurs through the initial formation of negative ion resonances. When going from d(A4) to d(A16), the strand break cross section increases with oligonucleotide length, but only at 7.0 and 8.4 eV, i.e., close to the maximum of the negative ion resonance, the increase in the strand break cross section with the length is similar to the increase of an estimated geometrical cross section. For d(A20), a markedly lower DNA strand break cross section is observed for all electron energies, which is tentatively ascribed to a conformational change of the dA20 sequence. The results indicate that, although there is a general length dependence of strand break cross sections, individual nucleotides do not contribute independently of the absolute strand break cross section of the whole DNA strand. The absolute quantification of sequence specific strand breaks will help develop a more accurate molecular level understanding of radiation induced DNA damage, which can then be used for optimized risk estimates in cancer radiation therapy.

The Role of Proton Transfer on Mutations.

Hydrogen bonds play a critical role in nucleobase studies as they encode genes, map protein structures, provide stability to the base pairs, and are involved in spontaneous and induced mutations. Proton transfer mechanism is a critical phenomenon that is related to the acid–base characteristics of the nucleobases in Watson–Crick base pairs. The energetic and dynamical behavior of the proton can be depicted from these characteristics and their adjustment to the water molecules or the surrounding ions. Further, new pathways open up in which protonated nucleobases are generated by proton transfer from the ionized water molecules and elimination of a hydroxyl radical in this review, the analysis will be focused on understanding the mechanism of untargeted mutations in canonical, wobble, Hoogsteen pairs, and mutagenic tautomers through the non-covalent interactions. Further, rare tautomer formation through the single proton transfer (SPT) and the double proton transfer (DPT), quantum tunneling in nucleobases, radiation-induced bystander effects, role of water in proton transfer (PT) reactions, PT in anticancer drugs–DNA interaction, displacement and oriental polarization, possible models for mutations in DNA, genome instability, and role of proton transfer using kinetic parameters for RNA will be discussed.

Low energy electron and positron impact differential cross sections for the ionization of water molecules in the coplanar and perpendicular kinematics.

We report here triply differential cross sections (TDCSs) for 81 eV electron and positron-impact ionization of the combined (1b1 + 3a1) orbitals of the water molecule by using the second-order distorted wave Born approximation (DWBA2) for ejection electron and positron energies of 5 eV and 10 eV and different momentum transfer conditions. The electron-impact TDCS will be compared with the experimental data measured by Ren et al. [Phys. Rev. A 95, 022701 (2017)] and with the molecular 3-body distorted wave (M3DW) approximation results in the scattering plane as well as the perpendicular plane. The DWBA2 results are in better agreement with the experiment than the M3DW results for the scattering plane, and the M3DW results are somewhat better for the perpendicular plane. This observation is explained in terms of collision interactions. The electron and positron TDCSs are indistinguishable in the scattering plane. In the perpendicular plane, the positron results are similar in shape, but smaller in magnitude. However, the difference reduces with increasing projectile scattering angle and increasing ejected electron energy.

Intermolecular dynamics of ultraconfined interlayer water in tobermorite: influence on mechanical performance.

Ultraconfined interlayer water within the tobermorite molecular structure is responsible for changes in the uniaxial tensile and compressive response of the family of tobermorites: 9, 11 and 14 Å. These confined interlayer water molecules are engaged in solvation of cations and anions within the tobermorite structure, which has been demonstrated through the intermolecular vibrational spectra and hydrogen bond lifetime of the water molecules. This study demonstrates that instead of ionization of water molecules (as proposed in an earlier study), breaking of hydrogen bonds of water is more plausible leading to solvation of ions within the molecular structure of tobermorite. A schematic of the coordinate covalent bonds between the water molecules and the cations and anions of the tobermorite structure has been proposed in this study.

Double ionization of water molecules by proton impact: the role of the direct ionization mechanism

The proton-induced double ionization process of water molecules is here theoretically investigated at high impact energy. The current 1st Born perturbative approach refers to an initial collisional state that both includes a target molecular wave function expressed as a single-center linear combination of atomic orbitals and a plane wave for describing the incident proton whereas the final collisional state is characterized by a scattered proton modeled by a plane wave and two ejected electrons modeled by Coulomb wave functions coupled via a Gamow factor. Total and partial cross sections are then provided and compared with existing experimental and theoretical data in considering the various dissociative channels. Additionally, a study of the energy dependence of the double ionization process is reported for impact energies ranging from 300 keV to 10 MeV.

Proton Collision on Deoxyribose Originating from Doubly Ionized Water Molecule Dissociation.

In this work, we studied the fragmentation dynamics of 2-deoxy-d-ribose (DR) in solution that arises from the double ionization of a water molecule in its primary hydration shell. This process was modeled in the framework of ab initio molecular dynamics. The charge unbalanced in the solvent molecules produces a Coulomb explosion with the consequent release of protons with kinetic energy in the few electronvolts range, which collide with the surrounding molecules in solution inducing further chemical reactions. In particular, we observe proton collisions with the solute molecule DR, which leads to a complete ring opening. In DNA, damage to the DR moiety may lead to DNA strand breaking. This mechanism can be understood as one of the possible steps in the radiation-induced fragmentation of DNA chains.

Kinetic modeling of streamer penetration into de-ionized water

Interest in plasma-liquid interaction phenomena has grown in recent years due to applications in plasma medicine, water purification, and plasma-hydrocarbon reforming. The plasma in contact with liquid is generated, for example, using the plasma jets or streamer discharges. The interaction between the streamer and water can cause both physical and chemical modifications of the liquid. In this paper, the interaction between an anode-directed streamer and the de-ionized water is studied using one-dimensional particle-in-cell Monte Carlo collisions model. In this model, plasma species in both gas and liquid phase are considered as the macro-particles. We find that the penetration of the streamer head into the liquid causes ionization of water molecules by electron impact, a process which is usually ignored in the fluid models. The main charge carriers in the liquid phase are negative water ions which agree with earlier experimental and computational modeling studies. Additionally, we observe an ion-rich sheath in the vicinity of the water surface on the gas side.

Studying Townsend and glow modes in an atmospheric-pressure DBD using mass spectrometry

Ambient molecular beam mass spectrometry has been employed to examine the effects of the mode of operation and the excitation waveform on the ionic content of a helium-based atmospheric-pressure parallel plate dielectric barrier discharge. By applying 10 kHz microsecond voltage pulses with a nanosecond rise times and 10 kHz sinusoidal voltage waveforms, distinctly different glow and Townsend modes were produced, respectively. Results showed a significant difference in the dominant ion species between the two modes. In the Townsend mode, molecular oxygen ions, atomic oxygen anions and nitric oxide anions are the most abundant species, however, in the glow mode water clusters ions and hydrated nitric oxygen anions dominate. Several hypotheses are put forward to explain these differences, including low electron densities and energies in the Townsend mode, more efficient ionization of water molecules through penning ionization and charge exchange with other species in glow mode, and large temperature gradients due to the pulsed nature of the glow mode, leading to more favorable conditions for cluster formation.

Fabrication of arrayed metal oxide structures by electrochemical local oxidation using metallic tip with electric field and humidity

Arrayed metal oxide structures were prepared using a simple metallic tip based local oxidation created by an electrochemical process between the metal tip and the substrate through ionized water molecules generated by a humidifier. CuO and WOx dots with diameter <1μm were fabricated using copper and tungsten tips, respectively. A potential bias >–20V with a humidity above 75% resulted in the formation of oxide dots. SEM, EDAX, XRD and laser Raman studies done on the fabricated structures confirmed the formation of metal oxide structures. The process of oxide formation and the effect of applied field and humidity on the property of oxide dot are studied.

Single ionization of water molecules in collisions with bare ions

We present the double differential cross sections (DDCSs) for the direct ionization of water molecules by impact of fully stripped helium, carbon and oxygen atoms, respectively. In the present formalism, we have represented the wavefunction in the entrance channel as the product of a plane wave for the projectile and an accurate one-center-molecular wavefunction of the water molecule by Moccia (1964 J. Chem. Phys. 40 2186). In the exit channel, we have expressed the total wavefunction as the product of pair-wise Coulomb wavefunctions among the ejected electron, projectile ion and the residual target ion, respectively. The contributions of DDCSs for five different molecular orbitals of water to the spectrum of angular distributions have been analyzed for several electron emission energies. The present results for DDCSs are compared with existing experimental and theoretical findings. We find an overall good agreement between our calculated results and the experimental findings for electron emission cross sections. In addition, DDCS results for ionization from different orbitals at a few electron emission energies are given in tabular form.

Double differential distribution of electron emission in the ionization of water molecules by fast bare oxygen ions

The doubly differential distributions of low-energy electron emission in the ionization of water molecules under the impact of fast bare oxygen ions with energy of 48 MeV are measured. The measured data are compared with two quantum-mechanical models, i.e. the post and prior versions of the continuum distorted wave–eikonal initial state (CDW-EIS) approximation, and the first-order Born approximation with initial and final wavefunctions verifying correct boundary conditions (CB1). An overall excellent qualitative agreement is found between the data and the CDW-EIS models whereas the CB1 model showed substantial deviation. However, the detailed angular distributions display some discrepancies with both CDW-EIS models. The single differential and total cross-sections exhibit good agreement with the CDW-EIS models. The present detailed data set could also be used as an input for modeling highly charged ion induced radiation damage in living tissues, whose most abundant component is water. Similar measurements are also carried out for a projectile energy of 60 MeV. However, since the double differential cross-section data show similar results the details are not provided here, except for the total ionization cross-sections results.

Enerhetychni vytraty na ionizatsiyu molekuly vody elektronnym udarom u slabkoionizovaniy plazmi

Enerhetychni vytraty na ionizatsiyu molekuly vody elektronnym udarom u slabkoionizovaniy plazmi

Equilibrium and Nonequilibrium Features in a Warm He+H2O Microwave Plasma at Atmospheric Pressure

A microwave surface-wave discharge at atmospheric pressure was generated using a He/H2O mixture and studied by optical emission spectroscopy. The main plasma parameters were determined based on the analysis of the spectra when partial thermodynamic equilibrium could be verified. The analysis showed that the system can be classified as a warm plasma with an average gas temperature of $1.7\times 10^{3}$ K, an axially averaged electron density of $2.4\times 10^{13}$ cm $^{-3}$ , and a semiempirically estimated average electron temperature of $15\times 10^{3}$ K. The experimental evidence and theoretical arguments suggest that the main source of ionization in this plasma is the electronic impact ionization of water molecules. An abnormal intensity in the O I [3p ${\,}^{3}\text{P}_{0,1,2}] \to [3{\mathrm{ s}}{\,}^{3}\text{S}^{\circ }_{1}$ ] transition was observed, revealing an overpopulation of the 3p $^{3}\text{P}_{0,1,2}$ states. This observation—which may be explored to obtain stimulated emission—was explained as an effect of the reabsorption of photons generated in the plasma by the H I Ly $_{\beta }$ emission by oxygen atoms (O $\text{I}{\,}^{3}\text{P}_{\mathrm {\mathbf {2}}} \to 3\text{d}{\,}^{3}{\rm D {^{\circ }}}_{1,2,3}$ transition), an effect generally known as photoexcitation by accidental resonance.

Calculation of FDCS for the low and intermediate energy ionization of water molecules

Triply differential cross sections for the electron induced ionization of the 3a1 and 1b1 orbitals of the water molecule are calculated within the distorted wave Born approximation. The distorted wave functions are numerically calculated by modelling both the initial and the final channels whereas single-center Slater type wave functions are used for describing the molecular target. A good agreement with the existing experimental data is obtained.

Double ionization of water molecules induced by swift protons

Experimental cross sections for single and double ionization of ${\mathrm{H}}_{2}\mathrm{O}$ by swift ${\mathrm{H}}^{+}$ with energy ranging from 0.3 to 2.0 MeV are reported. In this energy range the ionization is the dominant collision process and charge transfer reactions can be disregarded. A multihit coincidence technique is used to measure the ${\text{H}}^{+}+{\text{OH}}^{+}$ and ${\text{H}}^{+}+{\text{O}}^{+}$ fragmentation channels. Single- and double-hit differential measurements together with a semiempirical calculation allow separating quantitatively the prompt and Auger-like decay contributions to fragmentation following a vacancy in the $2{a}_{1}$ molecular orbital. Concerning the double-ionization channel, it is found that for lower energies the mechanism of a sequential double-electron removal, known as TS2, dominates. For energies above above 750 keV/u ionization resulting from a single vacancy followed by an Auger like deexcitation takes over the TS2, becoming the main contribution to the double-ionization cross section. Our results are compared to the electron-impact data within the same velocity range and also with theoretical calculations available in the literature.

Excitation of vibrational modes in the ionization of water molecule by XUV/X-ray radiation

SynopsisWe present a theoretical study of the vibrationally resolved core photoionization of the water molecule up to high photon energies. In order to understand the role of the coupled electron-nuclear motion in polyatomic molecules, we thus have implemented a new methodology to describe all vibrational modes of a polyatomic molecule. We show our preliminary results on the O(1s) photoionization, with special focus on the vibrationally resolved cross sections in a large range of photon energies, reaching up to 1500 eV.

Calculation of FDCS for the low and intermediate energy electron impact ioni-zation of water molecules

SynopsisFully differential cross sections (FDCS) results for the electron impact ionization of water molecules taking place from 1b1, 1b2 and 2a1 orbitals are presented. The FDCS calculations have been performed in second Born approximation.

Double differential cross sections for liquid water ionization by impact of fast electrons

SynopsisA theoretical study for the single ionization of water molecules in liquid phase by electron impact at high energies is presented. Through a first order model, we compute multiple differential cross sections considering an asymmetric coplanar geometry. The wavefunctions for a single liquid water molecule are obtained in a realistic way by using a Wannier orbital formalism. We compare our results with experiments for the vapor phase and previous theoretical results obtaining a good qualitative agreement.

Mean energy of water molecule ionization by electron impact

The cost of ionization of a water molecule by an electron impact is calculated on the basis of two models with identical initial data and compared with available data from the literature. The results of calculations show that the ionization cost for the model with a monoenergetic beam with E = 1000 eV is W = 25.26 eV; for the model taking into account the electron energy distribution function in a plasma with Te = 100 eV, this value is W = 16.85 eV.