Photoionization Bands of Cyanogen: Multi-Mode Vibronic Coupling and Renner-Teller Effects

Multi-mode vibronic coupling in the , , and electronic states of Cyanogen radical cation (C N ) is investigated with the aid of ab initio quantum chemistry and first principles quantum dynamics methods. The electronic degenerate states of Π symmetry of C N undergo Renner-Teller (RT) splitting along degenerate vibrational modes of π symmetry. The RT split components form symmetry allowed conical intersections with those from nearby RT split states or with non-degenerate electronic states of Σ symmetry. A parameterized vibronic Hamiltonian is constructed using standard vibronic coupling theory in a diabatic electronic basis and symmetry rules. The parameters of the Hamiltonian are derived from ab initio calculated adiabatic electronic energies. The vibronic spectrum is calculated, assigned and compared with the available experimental data. The impact of various electronic coupling on the vibronic structure of the spectrum is discussed.     

Development and Verification of a Diagnostic Technology for Waste Battery Deterioration Factors

We defined four major deterioration factors (electrolyte loss (EL), lithium loss (LL), lithium precipitation (LP), and compound deterioration (CD)). Then, we derived eleven key performance indicators (KPIs) for comparative analysis. After that, we fabricated three deteriorated cells for each of three deterioration factors (EL, LL, and LP) and one cell with CD (for verification) with four individual (dis)charging experiment manuals. The two major contributions of this study are the performance of 1) trend analysis to determine a suitable diagnostic metric by inspecting the eleven KPIs and 2) comparison analysis of and to verify the effectiveness of utilizing as a real-time deterioration diagnostic factor using a concept of model-in-the-loop simulation. The results show that 1) has the most conspicuous trendline tendency among the eleven comparison targets for all four major deterioration factors, and 2) the angle difference between the two trends of and lies within a minimum of 9° and a maximum of 43° (with a sscale on the x-axis and a scale on the y-axis for a clear trend line analysis). From this, we can conclude that the trendline-based real-time deterioration analysis employing may be practically applicable to a limited extent.     

Potential of AMnO3 (A=Ca,Sr, Ba,La) as Active Layer in Inorganic Perovskite Solar Cells

Inorganic perovskite CaMnO was proposed as a substitution for the TiO anatase in electron transport layers of solar cells containing the hybrid perovskite CH NH PbI based on increased mobility of electrons and better optical matching. Due to a suitable band gap concerning the absorption of sunlight, we investigate the potential of CaMnO and similar manganite perovskites, where Ca is replaced by either Sr, Ba or La, as an absorber layer in inorganic perovskite solar cells. In this study, we have used optical measurements on the synthesized AMnO (A=Ca, Sr, Ba, La) samples to aid density functional theory calculations (DFT) in order to accurately simulate the electronic and optical properties of AMnO compounds and gauge their potential for the role of absorber layer. Both experimental measurements and theoretical calculations show suitable band gap of 1.1-1.5 eV, depending on the compound, and absorption coefficients of the order of cm in the visible part of the spectrum.     

Reversible Metal-Hydride Transformation in Mg-Ti-H Nanoparticles at Remarkably Low Temperatures

We study the kinetics of hydrogen sorption in Mg-Ti-H nanoparticles prepared by gas phase condensation of mixed Mg-Ti vapors under a H₂-containing atmosphere. Four samples with different Ti contents from 14 to 63 at.% Ti are examined in the 100–150 °C range. The hydrogen absorption kinetics coupled with the formation of MgH₂ can be described by a nucleation and growth model. The activation energy is in the range kJ/mol and the rate constant (at 150 °C) increases from s⁻¹ to s⁻¹ with increasing Ti content. Hydrogen desorption is well modeled by a sequence of surface-limited and contracting-volume kinetics, except at the highest Ti content where nucleation and growth is observed. The activation energy of surface-limited kinetics is /mol. The rate constant (at 150 °C) increases from s⁻¹ to s⁻¹ with the Ti content. These results open an unexplored kinetic window for Mg-based reversible hydrogen storage close to ambient temperature.     

Investigating Possible Dipole-Bound States of Cyanopolyynes: the Case for the C5N− Anion Detected in Interstellar Space

We present results of quantum structure calculations aimed at demonstrating the possible existence of dipole-bound states (DBS) for the anion , a species already detected in the Interstellar medium (ISM). The positive demonstration of DBS existence using ab initio studies is an important step toward elucidating possible pathways for the formation of the more tightly bound valence bound states (VBS) in environments where free electrons from starlight ionization processes are known to be available to interact with the radical partner of the title molecule. Our current calculations show that such excited DBS states can exist in , in agreement with what we had previously found for the smallercyanopolyyne in the series: the anion. This system has a very weakly bound anion with binding energies of about 3 and 9 cm⁻¹ for the and DBS, respectively.     

The role of dimers in complex forming reactions at low temperature: full dimension potential and dynamics of (H2CO)2+OH reaction

The (H CO) +OH and H CO-OH+H CO reaction dynamics are studied theoretically for temperatures below 300 K. For this purpose, a full dimension potential energy surface is built, which reproduces well accurate ab initio calculations. The potential presents a submerged reaction barrier, as an example of the catalytic effect induced by the presence of the third molecule. However, quasi-classical and ring polymer molecular dynamics calculations show that the dominant channel is the dimer-exchange mechanism below 200 K, and that the reactive rate constant tends to stabilize at low temperatures, because the effective dipole of either dimer is reduced with respect to that of formaldehyde alone. The reaction complex formed at low temperatures does not live long enough to produce complete energy relaxation, as assumed in statistical theories. These results show that the reactivity of the dimers cannot explain the large rate constants measured at temperatures below 100 K.     

Combined Modelling of Triply Paired Electronic States of HO2+ ion with 3 Symmetry using Coupled Eigen Model

The multi state triply paired coupled adiabatic electronic states of , symmetries for the title ion have been modelled using the triply paired coupled eigen valued functions with the principal aim of getting a set of well optimized triply paired coupled functions, capable of explaining all the microscopic topograhical features present in the chosen coupled electronic states. The high quality size truncated dynamically correlated points at the limit of complete basis set (CBS) were utilized for this purpose. The proposed model function are presented in an “easy to understand” linear form with respect to the pre-defined variables which are directly dependent on the diabatic potentials and coupling strengths found in the diabatic matrix. Its most important feature (an essential criterion to be selected for modelling the triply degenerate seam pathway) is the ability to predict the existence of an uniquely defined triply degenerate iso-energetic geometry among the chosen coupled states in addition to the prediction of the existence of many doubly degenerate iso-energetic geometries in those states and hence can be adaptable to any general molecular system where such triply or doubly degenerate geometries are believed to occur. The title ion is one among them where many doubly iso-energetic geometries were located but not the triply degenerate one as it is a three atomic system unlike the polyatomic case where the triply degenerate geometry will most likely to be found. To do this work, one requires the knowledge of four asymptotic diatomic curves upon atom+diatom dissociation whose correct correlated spectroscopic states are O₂⁺ , O₂ , O₂⁺ , OH⁺ . The quality and the characteristics of analytical surface of the ion is discussed well in detail.     

Adsorption of Acetate on Au(111): An in-situ Scanning Tunnelling Microscopy Study and Implications on Formic Acid Electrooxidation

The adsorption of acetate on an Au(111) electrode surface in contact with acetic acid at pH 2.7 was imaged in-situ using scanning tunnelling microscopy (STM). Two different ordered structures were imaged for acetate adsorbed in the bidentate configuration on the unreconstructed surface at 0.95 V (vs. the saturated calomel electrode, SCE). The first structure, , is metastable and transforms at constant potential within 20 minutes to a structure, which is thermodynamically more favourable. The acetate adlayer starts to form at step edges and propagates via nucleation and growth onto terraces. The findings from in-situ STM are in agreement with the electrochemical behaviour of acetate on Au(111) characterized by voltammetry. A comparison is made with formate adsorption on Au(111). While acetate is not reactive, in contrast to formate, it can act as a spectator species in formic acid electrooxidation.     

Catalytic Reaction Mechanism of Bacterial GH92 α-1,2-Mannosidase: A QM/MM Metadynamics Study

The catalytic mechanism of a -dependent family 92 -mannosidase, which is abundantly present in human gut flora and malfunctions leading to the lysosomal storage disease α-mannosidosis, has been investigated using quantum mechanics/molecular mechanics and metadynamics methods. Computational efforts show that the enzyme follows a conformational itinerary of and the ion serves a dual purpose, as it not only distorts the sugar ring but also plays a crucial role in orchestrating the arrangement of catalytic residues. This orchestration, in turn, contributes to the facilitation of conformers for the ensuing reaction. This mechanistic insight is well-aligned with the experimental predictions of the catalytic pathway, and the computed energies are of the same order of magnitude as the experimental estimations. Hence, our results extend the mechanistic understanding of glycosidases.     

Fluorine Substitution of TCNQ Alters the Redox-Driven Catalytic Pathway for the Ferricyanide-Thiosulfate Reaction

Mechanistic variation in catalysis through substituent-based redox tuning is well established. Fluorination of TCNQ (TCNQ=tetracyanoquinodimethane) provides ~850 mV variation in the redox potentials of the and (n=0, 2, 4) processes. With , catalysis of the kinetically very slow ferrocyanide-thiosulfate redox reaction in aqueous solution occurs via a mechanism in which the catalyst is reduced to when reacting with which is oxidised to . Subsequently, reacts with to form and reform the catalyst, in another thermodynamically favoured process. An analogous mechanism applies with as a catalyst. In contrast, since the reaction of with is thermodynamically unfavourable, an alternative mechanism is required to explain the catalytic activity observed in this non-fluorinated system. Here, upon addition of , reduction of to occurs with concomitant oxidation of to , which then acts as the catalyst for oxidation. Thermodynamic data explain the observed differences in the catalytic mechanisms. (n=0, 4) also act as catalysts for the ferricyanide-thiosulfate reaction in aqueous solution. The present study shows that homogeneous pathways are available following addition of these dissolved materials. Previously, these (n=0, 4) coordination polymers have been regarded as insoluble in water and proposed as heterogeneous catalysts for the ferricyanide-thiosulfate reaction. Details and mechanistic differences were established using UV-visible spectrophotometry and cyclic voltammetry.     

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and its Relevance in Solar Geoengineering Models

SO₂ has been proposed in solar geoengineering as a precursor of H₂SO₄ aerosol, a cooling agent active in the stratosphere to contrast climate change. Atmospheric ionization sources can ionize SO₂ into excited states of , which quickly reacts with trace gases in the stratosphere. In this work we explore the reaction of with excited by tunable synchrotron radiation, leading to ( ), where H contributes to O₃ depletion and OH formation. Density Functional Theory and Variational Transition State Theory have been used to investigate the dynamics of the title barrierless and exothermic reaction. The present results suggest that solar geoengineering models should test the reactivity of with major trace gases in the stratosphere, such as H₂ since this is a relevant channel for the OH formation during the nighttime when there is not OH production by sunlight. OH oxides SO₂, triggering the chemical reactions leading to H₂SO₄ aerosol.     

The Threshold Photoelectron Spectrum of Fulvenone: A Reactive Ketene Derivative in Lignin Valorization

Unveiling reaction mechanisms by isomer-selective detection of reactive intermediates requires advanced spectroscopic knowledge. We study the photoionization of fulvenone (c-C₅H₄=C=O), a reactive ketene species relevant in catalytic pyrolysis of lignin, which was generated by pyrolysis of 2-methoxy acetophenone. The high-resolution threshold photoelectron spectrum (TPES) with vacuum ultraviolet synchrotron radiation revealed well-resolved vibrational transitions, assigned to ring deformation modes of the cyclopentadiene moiety. The adiabatic ionization energy was determined to be 8.25±0.01 eV and is assigned to the ²A₂← ¹A₁ transition. A broad and featureless band arising at 9 eV is associated with the ²B₁← ¹A₁ excitation. A conical intersection is responsible for the ultrafast relaxation of the fulvenone cation from the into the state resulting in a featureless and lifetime broadened band. These insights will increase the detection capabilities for fulvenone and thereby help to elucidate reaction mechanisms in lignin catalytic pyrolysis.     

Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C2−

Carbon 1s core-hole excitation of the molecular anion C₂⁻ has been experimentally studied at high resolution by employing the photon-ion merged-beams technique at a synchrotron light source. The experimental cross section for photo–double-detachment shows a pronounced vibrational structure associated with and core excitations of the C₂⁻ ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C₂⁻ molecular anion by 0.2 Å upon this core photoexcitation. The associated change of the molecule's moment of inertia leads to a noticeable rotational broadening of the observed vibrational spectral features. This broadening is accounted for in the present analysis which provides the spectroscopic parameters of the C₂⁻ and core-excited levels.     

Nanoscale Structure in Short-Chain Ionic Liquids

The temperature (T) and cationic chain length (n) evolution of the nanoscale structure of the sub-layering-threshold members of a model family of room temperature ionic liquids (RTILs) is investigated by x-ray scattering. The measured curves are computer-resolved into individual Teubner-Strey-like lineshapes. The polar-apolar layering is found to start at . Opposite n-trends are found at for the spacings and correlation lengths associated with the diffraction patterns’ two main peaks, and assigned to a shift of balance between the two main interactions, Coulomb and van der Waals, and to increasing packing constraints due to the addition of methylenes. The spacings’ thermal expansion coefficients are found to deviate from the macroscopically-measured values, and to anomalously decrease with increasing temperature. Finally, the reduced temperature scale, , ( melting temperature), is demonstrated to render the observed trends significantly more systematic than those on a conventional T scale.     

Trihydrogen Cation Helium Clusters: A New Potential Energy Surface

We present a new analytical potential energy surface (PES) for the interaction between the trihydrogen cation and a He atom, , in its electronic ground state. The proposed PES has been built as a sum of two contributions: a polarization energy term due to the electric field generated by the molecular cation at the position of the polarizable He atom, and an exchange-repulsion and dispersion interactions represented by a sum of “atom-bond” potentials between the three bonds of and the He atom. All parameters of this new PES have been chosen and fitted from data obtained from high-level ab-initio calculations. Using this new PES plus the Aziz-Slaman potential for the interaction between Helium atoms and assuming pair-wise interactions, we carry out classical Basin-Hopping (BH) global optimization, semiclassical BH with Zero Point Energy corrections, and quantum Diffusion Monte Carlo simulations. We have found the minimum energy configurations of small He clusters doped with , , with N=1–16. The study of the energies of these clusters allows us to find a pronounced anomaly for N=12, in perfect agreement with previous experimental findings, which we relate to a greater relative stability of this aggregate.     

Size Evolution of Photoabsorption Spectra of Small Clusters: A Computational Study

Photoabsorption spectra of clusters, N=5–9, have been calculated using a diatomics-in-molecules like electronic structure model and a path-integral Monte Carlo sampling method. A qualitative change in the calculated spectra has been observed at N=9, which has been interpreted in terms of a structural transformation in the clusters consisting in a transition from trimer-like ionic cores observed for N≤7 to dimer-like ionic cores prevailing in through an intermediate state (comparable abundances of both types of ionic cores) observed in . The calculated spectra have been thoroughly compared with an earlier calculation on , , and reported from our group and data available for the same cluster sizes from an experiment.     

Quantum Phase Diagram of a Frustrated Spin-1/2 Ferro-Antiferromagnetic Normal Ladder

In this work, we consider a frustrated two-leg spin-1/2 ladder composed of Heisenberg ferromagnetic and antiferromagnetic spin-1/2 chains, and nearest spins from different legs interact via Heisenberg type rung exchange interactions that can be either ferromagnetic or antiferromagnetic in nature. The competing exchange interactions in the system lead to five different quantum phases like ferromagnetic, non-collinear ferrimagnetic (NCF), , antiferromagnetic and dimer phases. The  quantum phase diagram is constructed for the Heisenberg spin-1/2 model and the phases are characterized using the correlation functions which are calculated by the density matrix renormalization group method. We also analyze the  stability of phase and calculate the pitch angle in the NCF phase.     

The Role of Hydrogen Bonds and Electrostatic Interactions in Enhancing Two-Photon Absorption in Green and Yellow Fluorescent Proteins

The spectral properties of fluorescent proteins (FPs) depend on the protein environment of the chromophore (CRO). A deeper understanding of the CRO – environment interactions in terms of FPs’ spectral characteristics will allow for a rational design of novel markers with desired properties. Here, we are taking a step towards achieving this important goal. With the time-dependent density functional theory (TDDFT), we calculate one- and two-photon absorption (OPA and TPA) spectra for 5 green FPs (GFPs) and 3 yellow FPs (YFPs) differing in amino acid sequence. The goal is to reveal the roles of: (i) electrostatic interactions, (ii) hydrogen-bonds (h-bonds) and (iii) h-bonds together with distant electrostatic field in absorption spectra tuning. Our results point to design hypothesis towards FPs optimised for TPA-based applications. Both h-bonds and electrostatic interactions co-operate in enhancing TPA cross-section ( ) for the transition in GFPs. Furthermore, it seems that details of h-bonds network in the CRO's vicinity influences response to CRO – environment electrostatic interactions in YFPs. We postulate that engineering FPs with more hydrophilic CRO's environment can lead to greater . We also find that removing h-bonds formed with the CRO's phenolate leads to TPA enhancement for transition to higher excited states than S₁. Particularly Y145 and T203 residues are important in this regard.     

Atomic-Scale Studies of Fe3O4(001) and TiO2(110) Surfaces Following Immersion in CO2-Acidified Water

Difficulties associated with the integration of liquids into a UHV environment make surface-science style studies of mineral dissolution particularly challenging. Recently, we developed a novel experimental setup for the UHV-compatible dosing of ultrapure liquid water and studied its interaction with TiO₂ and Fe₃O₄ surfaces. Herein, we describe a simple approach to vary the pH through the partial pressure of CO₂ ( ) in the surrounding vacuum chamber and use this to study how these surfaces react to an acidic solution. The TiO₂(110) surface is unaffected by the acidic solution, except for a small amount of carbonaceous contamination. The Fe₃O₄(001)-( × )R45° surface begins to dissolve at a pH 4.0–3.9 ( =0.8–1 bar) and, although it is significantly roughened, the atomic-scale structure of the Fe₃O₄(001) surface layer remains visible in scanning tunneling microscopy (STM) images. X-ray photoelectron spectroscopy (XPS) reveals that the surface is chemically reduced and contains a significant accumulation of bicarbonate (HCO₃⁻) species. These observations are consistent with Fe(II) being extracted by bicarbonate ions, leading to dissolved iron bicarbonate complexes (Fe(HCO₃)₂), which precipitate onto the surface when the water evaporates.     

Indirect Nuclear Spin-Spin Exchange Coupling through Solvated Electron in Small Sizes of Cyclic and Cage-Shaped Perfluoroalkanes

Small perfluorocycloalkanes (hexafluorocyclopropane (c-C₃F₆), octafluorocyclobutane (c-C₄F₈) and decafluorocyclopentane (c-C₅F₁₀) and cage-shaped perfluoroalkanes (perfluoro tetrahedral alkane (C₄F₄), perfluoro prismane (C₆F₆) and perfluoro cubane (C₈F₈)) are better electron scavengers. The captured excess electrons are weakly bound inside their backbone voids or over their backbones, forming the solvated electron ( ) systems (e@c-C_nF_2ns (n=3, 4, 5) and e@C_nF_n (n=4, 6, 8)). There have been many studies on the structures and properties of such systems. However, the effect of on the indirect nuclear spin-spin coupling (J-coupling) is unknown. In this work, we explore how affects ^NeJ-coupling between two coupled F nuclei (^NeJ_FF-coupling) in perfluoroalkane systems through density functional theory calculations. We find unusual trans-^NeJ_FF-couplings (two coupled F nuclei in trans-position) in e@c-C_nF_2n (n=3, 4, 5) and ^NeJ_FF-couplings in e@C_nF_n (n=4, 6, 8). One excess electron not only changes the molecular structures, but also enforces unique distributions and properties, depending on the structural characteristics. We also confirm that such unusual ^NeJ_FF-couplings are realized by through- (T-SE) transmission mechanism, rather than the conventional through-bonds (T−B)/through-space (T−S) ones. The novel transmission mechanism consists of the T-SE coupling path (path 1) and -enhanced T−B T−S coupling path (path 2), and the two paths jointly control ^NeJ_FF through cooperation and competition. Interestingly, the former plays a dominant role for long-range ^NeJ_FF-coupling (N=5), while the latter plays a role in the short-range ^NeJ_FF-coupling (N=3, 4). Path bending angle mainly influences path 1, while path 2 is mainly influenced by the path length. This work not only provides novel insights into the mediating role of in the coupling information exchange, but also proposes a new -based coupling mechanism, possibly opening up potential applications for the -based indirect nuclear spin couplings.