Spectroscopic Description Research Articles

Fine- and hyperfine structure semi-empirical studies of atomic cobalt. Even-parity configurations system

We present the results of multiconfiguration semi–empirical calculations of the fine structure (fs) and the hyperfine structure (hfs) for the even-parity level system of atomic cobalt (Co I), using all available experimental data. These results were obtained using our proprietary software package designed for complex atom structure analysis. Through the iterative fine-structure calculation procedure, predictions of energy levels along with their Landé gJ factors and wave functions were obtained for each electronic state. Good agreement was achieved between the theoretical hyperfine structures and the experimental constants, which confirmed the validity of the propositions in the spectroscopic descriptions of observed Co I levels. For some levels no experimental hfs constants were known; in such cases these values are predicted.

The lowest-lying Rydberg state of CdAr van der Waals complex: The improved characterization of the interatomic potential

Previous characterization of the double-well E3Σ1+63S1 - Rydberg state outer potential well E3Σ1out+ in CdAr van der Waals (vdW) complex has been based on detection of the E3Σ1+←B3Σ1+53P1 (υ″=0–2) transitions only. In this study, the gap in the limited characterization of the E3Σ1+out shallow well and the neighbouring potential barrier has been filled by recording bound (υ′) ← bound (υ″=1–4) and free ← bound (υ″=0–4) excitation spectra. The result, spectroscopic description of the E3Σ1out+ well along with the potential barrier have been concluded from simulations of the recorded spectra. The results were compared with those published previously.

Concise behavior of Curcumin in water-ethanol: Critical Water Aggregation Percentage and multivariate analysis of protolytic equilibria

Curcumin (CUR) is a promising natural product in the field of biomedical applications, having a range of pharmacological effects. Despite this, clinical trials have reported poor absorption, low bioavailability, and rapid metabolism, which reduce its effectiveness. In general, these problems are related to the highly hydrophobicity of CUR, a limiting factor not only in its applications but also in its characterization. In fact, the spectroscopic description of CUR in homogeneous/microheterogenous media has a range of controversies, mainly about its self-aggregation process and its pKa determinations. To solve these drawbacks, the present work describes the concise spectroscopic analysis of CUR in different water-ethanol mixtures. The Critical Water Aggregation Percentage (CWAP), i.e., the limit percentage in which monomers are predominant is 50% of water. The Multivariate Analysis that employs the chemometric tools (MASDA) by Q-mode method was efficient in demonstrating that above 75% (water: ethanol v/v) CUR exists predominantly in self-aggregated form. In addition, the molecular modeling conducted in the ORCA 4.2 using the Hartree-Fock method associated with MASDA demonstrated that even at 30% (water: ethanol v/v) CUR dimers are present (∼6%). From these conditions, the complex protolytic equilibria of CUR was evaluated in water-ethanol (30:70 v/v) with or without ionic strength. The pKa determination was also conducted by Multivariate Analysis. The obtained pKa values in the presence or absence of ionic strength control do not differ significantly. The protolytic equilibria can be represented in terms of the principal species: CUR0⇌ CUR−1 (enol/enolate), CUR−1⇌ CUR−2 (phenol/phenolate) and CUR−2⇌ CUR−3 phenol/phenolate). The chemometric also allows to obtain the spectra of the pure species and the molar absorptivity for each one. This set of results is especially important to complement the literature about the basic spectroscopy and physicochemical properties of CUR.

Molecular diatomic spectroscopy data

AbstractAccurate and comprehensive diatomic molecular spectroscopic data have long been vital in a wide variety of applications for measuring and monitoring astrophysical, industrial, and other gaseous environments. These data are also used extensively for benchmarking quantum chemistry and applications from quantum computers, ultracold chemistry and the search for physics beyond the standard model. Useful data can be highly detailed like line lists or summative like molecular constants, and obtained from theory, experiment, or a combination. There are plentiful (though not yet sufficient) data available, but these data are often scattered. For example, molecular constants have not been compiled since 1979 despite the existing compilation still being cited more than 200 times annually. Furthermore, the data are interconnected but updates in one type of data are not yet routinely applied to update interconnected data: in particular, new experimental and ab initio data are not routinely unified with other data on the molecule. This paper provides information and strategies to strengthen the connection between data producers (e.g., ab initio electronic structure theorists and experimental spectroscopists), data modelers (e.g., line list creators and others who connect data on one aspect of the molecule to the full energetic and spectroscopic description) and data users (astronomers, chemical physicists, etc.). All major data types are described including their source, use, compilation, and interconnectivity. Explicit advice is provided for theoretical and experimental data producers, data modelers, and data users to facilitate optimal use of new data with appropriate attribution.This article is categorized under: Theoretical and Physical Chemistry > Spectroscopy

Spectroscopic Description of the E1 State of Mo Nitrogenase Based on Mo and Fe X-ray Absorption and Mössbauer Studies.

Mo nitrogenase (N2ase) utilizes a two-component protein system, the catalytic MoFe and its electron-transfer partner FeP, to reduce atmospheric dinitrogen (N2) to ammonia (NH3). The FeMo cofactor contained in the MoFe protein serves as the catalytic center for this reaction and has long inspired model chemistry oriented toward activating N2. This field of chemistry has relied heavily on the detailed characterization of how Mo N2ase accomplishes this feat. Understanding the reaction mechanism of Mo N2ase itself has presented one of the most challenging problems in bioinorganic chemistry because of the ephemeral nature of its catalytic intermediates, which are difficult, if not impossible, to singly isolate. This is further exacerbated by the near necessity of FeP to reduce native MoFe, rendering most traditional means of selective reduction inept. We have now investigated the first fundamental intermediate of the MoFe catalytic cycle, E1, as prepared both by low-flux turnover and radiolytic cryoreduction, using a combination of Mo Kα high-energy-resolution fluorescence detection and Fe K-edge partial-fluorescence-yield X-ray absorption spectroscopy techniques. The results demonstrate that the formation of this state is the result of an Fe-centered reduction and that Mo remains redox-innocent. Furthermore, using Fe X-ray absorption and 57Fe Mössbauer spectroscopies, we correlate a previously reported unique species formed under cryoreducing conditions to the natively formed E1 state through annealing, demonstrating the viability of cryoreduction in studying the catalytic intermediates of MoFe.

Carbon chain extension processes in cryogenic environments: UV-assisted growth of polyynic nitriles in solidified rare gases

As demonstrated in recent years, polyynic nitriles may photochemically arise from smaller unsaturated chain species in an apparently rigid environment of a cryogenic rare gas matrix. Here I summarize the highlights of respective research that has advanced the spectroscopic description of R–(C≡C)n–C≡N molecules (R = H, CN or CH3).

The Penn State - Toruń Centre for Astronomy Planet Search stars

Context. Our knowledge of the intrinsic parameters of exoplanets is as precise as our determinations of their stellar hosts parameters. In the case of radial velocity searches for planets, stellar masses appear to be crucial. But before estimating stellar masses properly, detailed spectroscopic analysis is essential. With this paper we conclude a general spectroscopic description of the Pennsylvania-Toruń Planet Search (PTPS) sample of stars. Aims. We aim at a detailed description of basic parameters of stars representing the complete PTPS sample. We present atmospheric and physical parameters for dwarf stars observed within the PTPS along with updated physical parameters for the remaining stars from this sample after the first Gaia data release. Methods. We used high resolution (R = 60 000) and high signal-to-noise-ratio (S/N = 150–250) spectra from the Hobby-Eberly Telescope and its High Resolution Spectrograph. Stellar atmospheric parameters were determined through a strictly spectroscopic local thermodynamic equilibrium analysis (LTE) of the equivalent widths of Fe I and Fe II lines. Stellar masses, ages, and luminosities were estimated through a Bayesian analysis of theoretical isochrones. Results. We present Teff, log g, [Fe/H], microturbulence velocities, absolute radial velocities, and rotational velocities for 156 stars from the dwarf sample of PTPS. For most of these stars these are the first determinations. We refine the definition of PTPS subsamples of stars (giants, subgiants, and dwarfs) and update the luminosity classes for all PTPS stars. Using available Gaia and HIPPARCOS parallaxes, we redetermine the stellar parameters (masses, radii, luminosities, and ages) for 451 PTPS stars. Conclusions. The complete PTPS sample of 885 stars is composed of 132 dwarfs, 238 subgiants, and 515 giants, of which the vast majority are of roughly solar mass; however, 114 have masses higher than 1.5 M⊙ and 30 of over 2 M⊙. The PTPS extends toward much less metal abundant and much more distant stars than other planet search projects aimed at detecting planets around evolved stars; 29% of our targets belong to the Galactic thick disc and 2% belong to the halo.

Connection between the su(3) algebraic and configuration spaces: bending modes of linear molecules

ABSTRACTAn approach to connect the dynamical group – used to describe the bending modes of linear molecules – with configuration space is discussed. The group may be seen as a consequence of adding a scalar boson to the space of two degenerate harmonic oscillators. The resulting group becomes the dynamical group for 2D systems The connection of the model with configuration space however is not obvious. Our approach is based on establishing a mapping between the algebraic and configuration states. The identification in the algebraic space of coordinates and momenta leads to a new identification of the group chains: they are associated with energy, coordinate and momentum representations. In addition an analysis of local-to-normal mode transition is presented. This provides a criterion to decide between a local or normal mode descriptions in an spectroscopic description. As an example we consider the situation of the bending modes of acetylene taking a Hamiltonian up to quartic order. The different results for the force constants obtained from the local and normal mode treatments leads to the conclusions that previous applications of the bending modes of acetylene dealing with a local mode treatment is on the verge of applicability.

Two-photon probes for in vivo multicolor microscopy of the structure and signals of brain cells.

Imaging the brain of living laboratory animals at a microscopic scale can be achieved by two-photon microscopy thanks to the high penetrability and low phototoxicity of the excitation wavelengths used. However, knowledge of the two-photon spectral properties of the myriad fluorescent probes is generally scarce and, for many, non-existent. In addition, the use of different measurement units in published reports further hinders the design of a comprehensive imaging experiment. In this review, we compile and homogenize the two-photon spectral properties of 280 fluorescent probes. We provide practical data, including the wavelengths for optimal two-photon excitation, the peak values of two-photon action cross section or molecular brightness, and the emission ranges. Beyond the spectroscopic description of these fluorophores, we discuss their binding to biological targets. This specificity allows in vivo imaging of cells, their processes, and even organelles and other subcellular structures in the brain. In addition to probes that monitor endogenous cell metabolism, studies of healthy and diseased brain benefit from the specific binding of certain probes to pathology-specific features, ranging from amyloid-β plaques to the autofluorescence of certain antibiotics. A special focus is placed on functional in vivo imaging using two-photon probes that sense specific ions or membrane potential, and that may be combined with optogenetic actuators. Being closely linked to their use, we examine the different routes of intravital delivery of these fluorescent probes according to the target. Finally, we discuss different approaches, strategies, and prerequisites for two-photon multicolor experiments in the brains of living laboratory animals.

Comparative instrumental investigations of some bile acids

In this paper, we present the spectroscopic description (by the means of UATR-FTIR spectroscopy) for four naturally occurring bile acids, namely lithocholic acid (LC), taurocholic acid sodium salt hydrate (TC), taurodeoxycholic acid sodium salt hydrate (TDC) and chenodeoxycholic acid (CDC), as well as their thermal behaviour in dynamic oxidative atmosphere, by TG/DTG/HF means. It was shown that all samples have a good thermal stability, favourized by the presence of cholan-24-oic structural moiety in all samples, as well as the solid-state structure (intermolecular H-bondings for the carboxylic acids CDC and LC and saline structures for TDC and TC, respectively). These data are simple, but of great interest in identifying the presence of these compounds by fast, reproducible and precise instrumental techniques in complex mixtures, such as biliary stones.

A study of vibrational excitations of ozone in the framework of a polyad preserving model of interacting Morse oscillators

The vibrational spectroscopic description of the ozone molecule 16O3 in its electronic ground state X1A1 is presented in the framework of a simple local model, where Morse potentials are associated with both stretching and bending modes. The Hamiltonian is written in terms of internal coordinates considering the local mode character of the ozone molecule. Later on an algebraic representation in terms of Morse ladder operators is introduced through a linear approximation in the expansion of the coordinates and momenta. Three polyads are considered in our study: P11=ν1+ν3+ν2, P21=2(ν1+ν3)+ν2, and P32=3(ν1+ν3)+2ν2, as suggested by resonances derived from the fundamentals as well as from previous variational analysis. The best description is provided by the P11 polyad scheme, yielding an rms deviation of 1.85cm−1 for a fit involving 121 energy levels. Considering the other two polyads the description is less accurate: rms=2.78cm−1 for polyad P21 and rms=2.63cm−1 for polyad P32, considering 99 and 100 energy levels, respectively. These fits represent the best descriptions in the framework of an algebraic approach. In addition, since our algebraic model keeps the connection with configuration space, the force constants derived from the three fits have been estimated. We have found that all the available experimental energies may be assigned at least to one of the three fits. As the energy increases the eigenstates obtained from different polyad schemes differ. This fact paves the way to establish a polyad breaking approach as a next step to improve the description.

Site selective analysis of Nd3+–Lu3+codoped CaF2laser crystals

Within neodymium-doped laser crystals, the codoping of fluorite-type single crystals with non-optically active buffer ions reveals the possibility for broadband laser operation around 1 μm, which makes these materials appealing for a number of applications such as amplifiers for new generation laser fusion facilities. In this work, a detailed spectroscopic investigation of CaF2:Nd3+ single crystals co-doped with various concentrations of Lu3+ ions is presented. The results show that the Nd3+ emission quantum efficiency increases drastically with the Lu3+ concentration, as a consequence of the replacement of Nd3+–Nd3+ clusters by two predominant types of Nd3+–Lu3+ clusters. These two main Nd3+ emitting centres are characterized in detail by identifying, for the first time to the best of our knowledge, their individual absorption and emission cross-section spectra, along with their fluorescence and radiative lifetimes and respective concentrations. The identification of the two predominant Nd3+–Lu3+ clusters (labelled NL1 and NL2) is carried out at room temperature by carefully choosing the Lu3+ concentration, the time windows used in time-resolved spectroscopy and the excitation or emission wavelength. The determination of the different centre concentrations and respective absorption cross-sections is achieved by comparing selective time-resolved excitation spectra and absorption spectra encompassing contributions from Nd–Nd clusters and the two types of Nd3+–Lu3+ clusters. As the Lu3+ concentration increases, the NL2 centres become predominant and are characterized by an emission peak at 1054 nm and a stronger emission cross-section than that of their NL1 counterparts. Finally, the absorption cross-sections, concentrations and lifetimes are successfully used to calculate the contributions of NL1 and NL2 in the various emission spectra regardless of the Lu3+ concentration or excitation wavelength confirming the consistency of the spectroscopic description.

Vibrational dynamics. Experimental ground-state combination differences of CH₅⁺.

Protonation of methane (CH4), a rather rigid molecule well described by quantum mechanics, produces CH5(+), a prototypical floppy molecule that has eluded definitive spectroscopic description. Experimental measurement of high-resolution spectra of pure CH5(+) samples poses a formidable challenge. By applying two types of action spectroscopy predicated on photoinduced reaction with CO2 and photoinhibition of helium cluster growth, we obtained low-temperature, high-resolution spectra of mass-selected CH5(+). On the basis of the very high accuracy of the line positions, we determined a spectrum of combination differences. Analysis of this spectrum enabled derivation of equally accurate ground state-level schemes of the corresponding nuclear spin isomers of CH5(+), as well as tentative quantum number assignment of this enfant terrible of molecular spectroscopy.

Nuclear structure aspects of spin-independent WIMP scattering off xenon

We study the structure factors for spin-independent WIMP scattering off xenon based on state-of-the-art large-scale shell-model calculations, which are shown to yield a good spectroscopic description of all experimentally relevant isotopes. Our results are based on the leading scalar one-body currents only. At this level and for the momentum transfers relevant to direct dark matter detection, the structure factors are in very good agreement with the phenomenological Helm form factors used to give experimental limits for WIMP-nucleon cross sections. In contrast to spin-dependent WIMP scattering, the spin-independent channel, at the one-body level, is less sensitive to nuclear structure details. In addition, we explicitly show that the structure factors for inelastic scattering are suppressed by ~ 10^{-4} compared to the coherent elastic scattering response. This implies that the detection of inelastic scattering will be able to discriminate clearly between spin-independent and spin-dependent scattering. Finally, we provide fits for all calculated structure factors.

Polyakov loop spectroscopy in the confined phase of gluodynamics and QCD

By using a simple relativistic model, we compute the glueball and gluelump spectra and relate these quantities, respectively, to the trace anomaly and Polyakov loop in the adjoint representation of gluodynamics. This spectroscopic description of thermodynamics is extended with the inclusion of quarks. The relation between the hadron resonance gas and the Polyakov loop in the fundamental and higher representations is addressed.

Study on the interaction between amphiphilic drug and bovine serum albumin: A thermodynamic and spectroscopic description

Herein we report the interaction of amphiphilic drug clomipramine hydrochloride (CLP—a tricyclic antidepressant) with bovine serum albumin (BSA) studied by fluorescence, UV–vis, and circular dichroism (CD) spectroscopic techniques. Clomipramine hydrochloride is used to treat a variety of mental health problems. The quenching rate constant (kq) values, calculated according to the fluorescence data, decrease with increase in temperature indicating the static quenching procedure for the CLP–BSA interaction. The association binding constants (KA), evaluated at different conditions, and the thermodynamic parameters (free energy, enthalpy and entropy changes) indicate that the hydrophobic forces play a major role in the binding interaction of drug. The interaction of BSA with CLP was further confirmed by UV absorption spectra. Blue shift of position was detected due to the complex formation between the BSA–CLP. The molecular distance, r0, between donor (BSA) and acceptor (CLP) was estimated by fluorescence resonance energy transfer (FRET) whose value (4.47nm) suggests high probability of static quenching interaction. The CD results prove the conformational changes in the BSA on binding with the drug. Thus, the results supply qualitative and quantitative understanding of the binding of BSA to CLP, which is important in understanding their effect as therapeutic agents.

An algebraic approach applied to the determination of the polarizability in CO2

A local algebraic approach to describe vibrational excitations of molecules presenting both local and normal mode behaviors is presented. This approach allows the connection with configuration space to be established. The model consists in expanding the kinetic energy as well as the potential in terms of coordinates and momenta. An algebraic representation is obtained by introducing creation and destruction bosonic operators associated with the harmonic oscillators. From the resulting Hamiltonian a local algebraic representation is obtained through a canonical transformation to local bosonic operators. Finally an anharmonization is carried out by changing the local bosonic operators to ladder operators associated with the Morse or Pöschl-Teller functions. Since the model is connected with configuration space, non linear curvilinear coordinates are contemplated. Our model is applied to the vibrational spectroscopic description of the 12C16O2 molecule. The eigenstates are tested by calculating the derivatives for the polarizability for this molecule.

Hyperfine structure and isotope shift measurements of unclassified lines in Eu II and new determination of the partition function

Results of the measurements of isotope shifts and the hyperfine structure for 31 unclassified spectral lines of Eu II, obtained with the laser-induced fluorescence method, are presented. All experimental results are the first results available for these spectral lines. On the basis of measured hyperfine structure constants, J quantum numbers and fluorescence channels (by comparison to the theoretically predicted values), identification of electronic levels was accomplished. The lower levels of the lines investigated were identified as levels belonging to configuration 4f76s. On the basis of the literature values of isotope shifts for this configuration, isotope shifts for lower and upper levels were determined, and, with the use of a sharing rule, contributions of particular configurations in the spectroscopic description of these levels were evaluated. The number of configurations (cores) necessary for description of the Eu II spectrum and the resulting changes of partition function were estimated. Although, due to the lack of transitions to known electronic levels in Eu II, determination of absolute energies of the levels identified was impossible, probable energy values are presented, which might constitute a starting point for investigations in other spectral regions.

Large-scale nuclear structure calculations for spin-dependent WIMP scattering with chiral effective field theory currents

We perform state-of-the-art large-scale shell-model calculations of the structure factors for elastic spin-dependent WIMP scattering off 129,131Xe, 127I, 73Ge, 19F, 23Na, 27Al, and 29Si. This comprehensive survey covers the non-zero-spin nuclei relevant to direct dark matter detection. We include a pedagogical presentation of the formalism necessary to describe elastic and inelastic WIMP-nucleus scattering. The valence spaces and nuclear interactions employed have been previously used in nuclear structure calculations for these mass regions and yield a good spectroscopic description of these isotopes. We use spin-dependent WIMP-nucleus currents based on chiral effective field theory (EFT) at the one-body level and including the leading long-range two-body currents due to pion exchange, which are predicted in chiral EFT. Results for all structure factors are provided with theoretical error bands due to the nuclear uncertainties of WIMP currents in nuclei.

THERMAL AND CHEMICAL STRUCTURE VARIATIONS IN TITAN'S STRATOSPHERE DURING THECASSINIMISSION

We have developed a line-by-line Atmospheric Radiative Transfer for Titan code that includes the most recent laboratory spectroscopic data and haze descriptions relative to Titan's stratosphere. We use this code to model Cassini Composite Infrared Spectrometer data taken during the numerous Titan flybys from 2006 to 2012 at surface-intercepting geometry in the 600-1500 cm–1 range for latitudes from 50°S to 50°N. We report variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE). We find indication for a weakening of the temperature gradient with warming of the stratosphere and cooling of the lower mesosphere. In addition, we infer precise concentrations for the trace gases and their main isotopologues and find that the chemical composition in Titan's stratosphere varies significantly with latitude during the 6 years investigated here, with increased mixing ratios toward the northern latitudes. In particular, we monitor and quantify the amplitude of a maximum enhancement of several gases observed at northern latitudes up to 50°N around mid-2009, at the time of the NSE. We find that this rise is followed by a rapid decrease in chemical inventory in 2010 probably due to a weakening north polar vortex with reduced lateral mixing across the vortex boundary.