Td Molecule Research Articles

A low fraction electrolyte additive as interface stabilizer for Zn electrode in aqueous batteries

The electrochemical performance of Zn metal anode in aqueous batteries is challenged by serious parasitic reactions and dendrite growth. Herein, we introduce an interface stabilizer of 2,3,4,5-tetrahydrothiophene-1,1-dioxide (TD), with a low volume fraction of 0.5%, in the 3 m ZnSO4 electrolyte for zinc batteries. Theoretical calculations and experimental analysis confirm the adsorption of TD molecules on Zn surface, which inhibits the spontaneous chemical corrosions by mildly acidic electrolytes and ensures a homogeneous electrode surface. The adsorbed TD further induces a stable solid-electrolyte interface (SEI) composed of organic sulfone/sulfonate species and inorganic zinc salts. The parasitic reactions are further suppressed. Meanwhile, the Zn2+ flux is homogenized in SEI, and uniform Zn deposition is realized. In the ZnSO4 electrolyte with 0.5% TD additive, stable Zn plating-stripping is achieved for 2500 h at 5 mA cm−2 and 2 mAh cm−2, which is 20 times longer than in the TD free electrolyte. Moreover, the Zn//V6O13·H2O full batteries with limited anode of N/P = 4 and N/P = 1.3 realize 93.8% and 75.0% capacity retentions, respectively, after 200 cycles with the 0.5% TD electrolyte, superior to 74.3% and 43.6% with the TD free electrolyte. Our work presents an effective strategy to promote the stability of Zn electrode for high performance aqueous batteries.

High-order contact transformations of molecular Hamiltonians: general approach, fast computational algorithm and convergence of ro-vibrational polyad models

The paper describes methods and fast computational algorithm for building effective Hamiltonians in molecular physics using perturbative approach. Separations of fast and slow variables are considered in the framework of contact transformations (CT). The particular focus is on a systematic derivation of effective models for rovibrational spectroscopy from ab initio-based potential energy surfaces with an exhaustive review of previous studies in this field. We consider applications to several types of polyads coupled by Fermi, Coriolis, Darling-Dennison and other types of resonance interactions with examples for asymmetric top, symmetric top and spherical top molecules. A flexible choice of the modelling operator accounts for strong couplings of various types of nuclear motion in molecules among closely lying levels including vibrational resonance schemes (2:1:2 . ), (2:1:2:1), (4:2:6:3), (3:2:1:2:1:1), etc. that occur for C2v, C3v and Td molecules and their isotopic species. The method is implemented in the MOL_CT programme suite, which offers a complementary tool to variational methods in terms of convergence and computational time. The range of applications is also different. The goal of the CT method is providing mathematical models for analyses of molecular spectra with the high-resolution accuracy using physically meaningful parameters derived from ab initio functions.

Long-range, collision-induced dipoles of Td–D∞h molecule pairs: Theory and numerical results for CH4 or CF4 interacting with H2, N2, CO2, or CS2

Compressed gases and liquids containing molecules of Td and D∞h symmetry absorb far-infrared radiation, due to transient dipole moments induced during molecular collisions. In earlier theoretical work on far-infrared absorption by CH4/N2 mixtures, good agreement was obtained between calculated and experimental spectra at low frequencies, but at higher frequencies—from 250 to 650 cm−1—calculated absorption intensities fell significantly below the experimental values. In this work, we focus on an accurate determination of the long-range, collision-induced dipoles of Td⋯D∞h pairs, including two polarization mechanisms not treated in the earlier line shape analysis: dispersion and nonuniformity in the local field gradient acting on the Td molecule. Since these mechanisms produce transitions with ΔJ=±3 or ±4 for CH4 and ΔJ=0 or ±2 for N2, their inclusion is expected to increase the calculated absorption intensities in the high frequency wings for CH4/N2 mixtures. This should improve agreement with the experimental spectra, and permit more accurate determination of anisotropic overlap terms in the collision-induced dipole. We give numerical values for the long-range dipole coefficients of CH4 or CF4 interacting with H2, N2, CO2, or CS2; the dipole coefficients have been derived with spherical-tensor methods and evaluated using single-molecule moments and susceptibilities from recent ab initio calculations or experiments. The dispersion dipoles are given rigorously in terms of integrals involving the imaginary-frequency polarizability α(iω) and the hyperpolarizabilities β(0;iω,−iω) and B(0;iω,−iω). To obtain numerical estimates for the dispersion dipoles, we have developed constant-ratio approximations that require only the static susceptibilities and C6 van der Waals coefficients.

Binding site on pea chloroplast fructose-1,6-bisphosphatase involved in the interaction with thioredoxin.

When we compare the primary structures of the six chloroplast fructose-1,6-biophosphatases (FBPase) so far sequenced, the existence of a poorly conserved fragment in the region just preceeding the redox regulatory cysteines cluster can be observed. This region is a good candidate for binding of FBPase to its physiological modulator thioredoxin (Td), as this association shows clear differences between species. Using a cDNA clone for pea chloroplast FBPase as template, we have amplified by PCR a DNA insert coding for a 19 amino acid fragment (149Pro-167Gly), which was expressed in pGEMEX-1 as a fusion protein. This protein strongly interacts with pea Td m, as shown by ELISA and Superose 12 gel filtration, depending on pH of the medium. Preliminary assays have shown inhibition of FBPase activity in the presence of specific IgG against the 19 amino acid insert. Surprisingly the fusion protein enhances the FBPase activation in competitive inhibition experiments carried out with FBPase and Td. These results show the fundamental role played by this domain in FBPase-Td binding, not only as docking point for Td, but also by inducing some structural modification in the Td molecule. Taking as model the structural data recently published for spinach photosynthetic FBPase, this sequence from a tertiary and quaternary structural point of view appears available for rearrangement.

Auger electron spectroscopy of molecules: Theory for angular and spin correlations with photoelectrons

This paper introduces a theory to interpret future experiments to simultaneously observe angular distribution of spin-resolved Auger and photoelectrons from a molecule belonging to one of the 32 point groups. The Auger electrons are emitted in the decay of the vacancy created by photoionization. We show that the desired correlation can be completely characterized by 12 parameters which are coefficients of trigonometric functions of the spherical angles of spin quantization directions of two outgoing electrons. The expressions for the parameters themselves, although reduced to the simplest possible forms by using the symmetry properties of the molecular point group to maximum advantage, depend upon bipolar harmonics involving the propagation directions of the Auger and photoelectrons. The angular and spin correlation function thus obtained is completely general and can be readily specialized to any experimental geometry used to observe the ejected electrons. In particular, it is found that for a linear experimental arrangement with spins oriented longitudinally to the respective propagation vectors of the two electrons moving out in opposite directions, the parameters become geometry independent with their number reducing to three, which are now coefficients of the first three Legendre polynomials. Correlation between the spin-quantization directions of Auger and photoelectrons is, on the other hand, described by six parameters which do not depend upon the experimental arrangement. Directional correlation between the two outgoing electrons has also been studied without observing their spins. These angular and/or spin correlation functions are shown to take particularly simpler forms for Auger and photoelectrons emitted from linear molecules. We have applied the procedures developed in this paper to study directional correlation between photoelectrons from 2a1 orbital in a Td molecule and the Auger electrons emitted in the decay of the consequent vacancy.

Photoelectron spectroscopic studies of polyatomic molecules: Degree of orientation and ionization of rotationally state selected, oriented molecules

In this paper we report theoretical studies of angle-resolved photoelectron spectroscopy (ARPES) and of circular dichroism in photoelectron angular distribution (CDAD) for ionization in molecules oriented in a single ‖JKJMJ〉 rotational eigenstate. These processes have been investigated also as two of the possible alternatives to photodissociation to determine orientational distribution function of rotationally state selected, oriented molecules. Expressions are derived which can be used to calculate ARPES and CDAD for such molecular species from ab initio methods or to analyze these experimentally observed spectra for extracting information about the degree of orientation of the molecular framework. These formulas are put in their simplest possible forms using the transformation properties of the molecular point group to their full advantage. The ionization amplitude is thus shown to decompose into a sum of transitions each involving the final state wave function belonging to an irreducible representation of the point group of the target molecule. It is found that, similar to the case of photodissociation, one can determine the rotational quantum number J purely from experimental photoionization data. Expressions developed herein are used to study ARPES and CDAD for ionization in a1 orbital of those rotationally state selected and oriented spherical top molecules which transform according to the Td point symmetry group. In this case, the detection-integrated cross section, singly differential in molecular orientation, is found to be independent of the photoionization dynamics and directly gives the molecular orientational function. The other ARPES and CDAD formulas are shown to depend upon the dynamics through the integrated partial cross section σ̄, the angularly asymmetry parameter β̄, the phase shift of the continuum waves representing the photoelectron, and the phase of the dipole transition amplitudes. The formulation presented in this paper sets a methodology for the analysis of measurements and calculation of the photoelectron spectra in rotationally state selected and oriented molecules in general, spherical top Td molecules in particular. It is applied, as an example, to photoionization in 6a21 orbital of oriented CCl4 in a pure ‖JKJMJ〉 rotational state. We find, among other things, that the photoelectron angular distributions change significantly when either or both of the directions of molecular orientation and of polarization of ionizing radiation vary from parallel to perpendicular to the quantization axis.

Photoelectron spectroscopic studies of polyatomic molecules: Detection-integrated cross sections for ionization in fixed T d systems

We have, in this paper, derived expressions for the partial photocurrent produced by ionization in the electric dipole approximation in an orbital of an oriented polyatomic molecule. The cross-section formulas, which are integrated over all directions of ejection of the photoelectron but differential with respect to the direction of the fixed molecular axis, are obtained in their simplest possible forms by taking full account of the transformation properties of the point symmetry group of the target and are thus applicable to photoionization in any oriented molecule belonging to one of the 32 point groups. The theory, as an example, has been applied to photoionization in a1 orbital of those oriented nonlinear systems whose point symmetry group is Td. This application shows that the singly differential, detection-integrated partial cross section for ionization by unpolarized, linearly or circularly polarized light in a1 orbital of a fixed Td molecule is (i) independent of the direction of its axis and (ii) equal to that averaged over all orientations of the target in space. Both conclusions are in agreement with recent experimental measurements on photoionization in 6a21 orbital of fixed CCl4. These results, in turn, are shown to mean that the variations with respect to the orientation of a molecule in space, found in theoretical calculations of photoelectron angular distribution for ionization in a1 valence orbitals of some of the Td targets, are due completely to the terms which stem from freezing both the molecular axis and the photoelectron detector in space. These terms completely vanish on integrating over all directions of propagation of the photoelectron, resulting in a current which is isotropic with respect to the orientation of the molecular axis in space. In such cases, it is therefore necessary to study the angular distribution of electrons ejected by photoionization in oriented molecules in order to obtain cross sections which will change with the direction of the target axis.

Photoelectron spectroscopic studies of polyatomic molecules: Angular distributions for ionization in oriented T d systems

A recently developed theory for angular distribution of electrons ejected by interaction of light with nonlinear molecules held fixed in space has been used to study ionization in a1 orbital of those systems which transform like the Td point symmetry group. Expressions for photoelectron angular distributions in the dipole approximation with the electric vector in the radiation beam both perpendicular and parallel to the molecular axis are derived. The properties of the two formulas, which are found to have completely different structures, have been studied. These expressions are shown to depend not only on all those quantities [i.e., the partial integrated cross-section σ̄, the asymmetry parameter β̄, and the polar angle θ of the propagation vector k (k,θ,φ) of the ejected electron] which are present in photoionization of an unoriented molecule, but involve in certain cases also the azimuthal angle φ, phase shifts of the continuum waves representing the outgoing electron, and the phase of the dipole transition amplitudes. Such fixed-molecule photoelectron angular distributions will therefore provide more stringent tests of theoretical models and probes of photoionization dynamics than the hitherto performed gas phase experiments on randomly oriented targets. They can also be used to identify the orientation of a molecule and/or geometry of a chemisorption site. The formulation presented here sets a frame work for the analysis of measurements and the calculations of spectra in those Td molecules which are fixed in space. We have applied it, as an example, to ionization in 4a1, 6a1, and 7a1 orbitals of oriented CF4, CCl4, and SiCl4, respectively. Without doing any dynamical calculations, using instead the experimentally measured values of σ̄ and β̄ as a function of the photon wavelength, the variations in the angular distributions with respect to the energy of the ejected electron as well as to the angles (θ,φ) and to the phases (which are treated as parameters) involved have been studied in detail. These distributions are found to have very rich and complicated structures arising from the spectral, angular, and/or phase variations of the angular momentum composition of the photocurrent.

The infrared spectra of matrix isolated thorium and uranium tetrachlorides. Change of shape with matrix gas

When thorium or uranium tetrachlorides are isolated in neon matrices, the spectra can be interpreted in terms of a Td molecule with a small site effect. Spectra obtained using sputtering techniques to generate ThCl4 in argon matrices agreed with those obtained previously using conventional vaporisation techniques. Detailed calculations of the i.r. spectra of isotopically enriched and natural abundance Th35/37Cl4 show that in krypton ThCl4 is not tetrahedral.

The vibrational spectra of some tetrachlorides in rare gas matrices with particular reference to the molecular shapes of ThCl4 and UCI4

Infrared spectra of tin, lead, hafnium, thorium, and uranium tetrachlorides isolated in inert gas matrices are reported. The results obtained for the tin, lead, and hafnium compounds follow the expected isotope patterns for a tetrahedral molecule except for the observation of additional weak features to high frequency of the all-35Cl isotopomers. By contrast for thorium tetrachloride the observed spectrum is not characteristic of a Td molecule but can be fitted to a species with C2v symmetry. Similar results (although less detailed) were obtained for uranium tetrachloride.

Vibrationally induced nuclear quadrupole coupling in tetrahedral and octahedral molecules

Hyperfine splittings arising from the presence of a quadrupolar nucleus at the center of a molecule belonging to the point group Td or Oh (e.g., 189OsO4 or 235UF6) are symmetry forbidden to a high degree of approximation. Nevertheless, quadrupole splittings can be induced by either vibrational or rotational distortions of the molecule, i.e., by distortions similar to those responsible for inducing electric dipole moments in Td molecules. Such hyperfine splittings have recently been observed in several laboratories using laser saturation spectroscopy. In this paper we investigate theoretically the quadrupole splittings induced by excitation of doubly and triply degenerate vibrations in Td and Oh molecules. We find that much of the vibration–rotation formalism already present in the methane literature can be applied with only minor changes to the induced-quadrupole-coupling problem, and that rather simple theoretical relationships can be derived between the quadrupole splitting and the tetrahedral or octahedral vibration–rotation splitting of a given level. Values for the scalar and tensor contribution to the quadrupole coupling constant have been derived from the experimental data for 189OsO4 reported by Bordé et al.

Folyl polyglutamate and folate-requiring enzymes as bacteriophage T4D baseplate structural components

The hexagonal-shaped baseplate on the tail of Escherichia coli bacteriophage T4D has been shown to contain 5–6 molecules of an unusual form of folic acid, dihydropteroyl hexaglutamate. In addition to this viral-induced small molecule, 2 viral-induced folate-requiring enzymes, namely dihydrofolate reductase ( frd) and thymidylate synthetase ( td), have also been found as phage baseplate components. The pteridine portion of the folate has been located near the baseplate frd and td and all 3 components are partially covered by T4D gene product 11 (gp11) which lies largely on the distal surface of the baseplate. On the other hand, the polyglutamate portion of the baseplate folic acid lies under or near the attachment region for the long tail fibers. Recent results have shown that the baseplate frd is a component of the outer wedge-like structures of the baseplate and highly suggestive evidence has now been obtained that the td molecule is a component of the central plug of the baseplate. These findings support the hypothesis that the baseplate folate plays a unique role in linking together the baseplate wedges and central plug by binding simultaneously to the wedge frd and to the plug td. This structural role for the viral folate and folate-requiring enzymes indicates that these baseplate components are not acting primarily in their usual roles as a coenzyme or as enzymes but are participants in a unique biological assembly process. Some molecular properties of dihydropteroyl hexaglutamate are presented which bear on its binding energies as a structural linking element. Finally some speculation is offered on the abiogenic origin of pteridine compounds.

Matrix-Isolation Infrared and Computer-Simulation Spectra (ν3 Bands) of GeCl4, GeBr4, and GeI4 in Argon Matrices

A tetrahedral MCl4 type molecule in which M is isotopically pure and Cl is in natural abundance consists of five isotopic species due to the mixing of the 35Cl (75.4%) and 37Cl (24.6%) isotopes. Table I lists their symmetry, percent natural abundances, and symmetry species of infrared active modes corresponding to the v3 vibration of the Td molecule. The v3 bands of CCl4 and 28SiCl4 in argon matrices exhibit five-peak chlorine isotope patterns due to overlap of the nine bands listed in Table I. The vertical lines shown in Fig. 1A' indicate such a pattern for 74GeCl4.

Forbidden rotational spectra of polyatomic molecules: Stark effects and Δ J = 0 transitions of Td molecules

The Δ J = 0 matrix elements of the centrifugally induced dipole moment of tetrahedral molecules in the ground vibrational state are examined. The predicted effects of these matrix elements are linear Stark effects of the E rotational levels and a complicated pure rotational spectrum in the radiofrequency and microwave regions. Tables of the centrifugal fine-structure splitting function, the linear Stark coefficients, and the line strengths of the E- E transitions and the stronger A- A and F- F transitions are presented for J values up to 20. The possible observation of these effects in methane is discussed.