Experimental Spectroscopic Parameters Research Articles

Thermal Responses and the Energy Spectral of Diatomic Molecules Using Nikiforov–Uvarov Methodology

The parametric Nikiforov–Uvarov approach and the Greene–Aldrich approximation scheme were used to achieve approximate analytical solutions to the Schrödinger equation, involving an interaction of the modified deformed Hylleraas potential mixed linearly with the improved Frost–Musulin diatomic molecular potential. For each ℓ-state, the energy spectra and normalized wave functions were generated from the hypergeometric function in the closed form. The thermal properties of such a system, including the vibrational partition function, vibrational mean energy, vibrational mean free energy, vibrational specific heat capacity, and vibrational entropy, were then calculated for the selected diatomic molecules using their experimental spectroscopic parameters. Furthermore, the peculiar conditions of this potential were evaluated, and their energy eigenvalues were calculated for the purpose of comparison. The acquired results were found to be in reasonable agreement with those reported in the literature.

Nd3+ doped titanate-germanate glasses for near-IR laser applications

In current work, spectroscopic properties of Nd3+ ions in titanate-germanate glasses have been studied for near-IR luminescence and laser applications. Near-IR luminescence at 1.06 µm due to 4F3/2 → 4I11/2 laser transition of Nd3+ ions has been examined in the function of TiO2 concentration. Based on theoretical calculations and experimental investigations, several spectroscopic and laser parameters for Nd3+ ions in titanate-germanate glasses were determined and compared to the previous results published for similar glass systems. Our systematic studies indicate that Nd3+ doped glass with molar ratio GeO2:TiO2 = 2:1 presents excellent near-IR luminescence properties and could be successfully applied to laser technology.

Unveiling the structural and energetic properties of thiazole-water complex by microwave spectroscopy and theoretical calculations.

The structure and non-covalent bonding features of the complex of thiazole and water were studied by using supersonic jet Fourier transform microwave spectroscopy and theoretical calculations. One isomer was observed which corresponds to the global minimum of the complex predicted theoretically. The rotational spectra of 9 additional isotopologues, including 5 mono-substituted heavy atoms of thiazole (34S, 13C and 15N), and 4 water isotopic species (H218O, DOH, HOD and D2O), were also measured and analyzed. The experimental spectroscopic parameters were used to determine the structural parameters of the observed isomer. Theoretical analyses based on quantum theory of atoms in molecules and natural bond orbital revealed that the two moieties are linked by a N···H-O hydrogen bond. The total interaction energy of the complex is calculated to be -25.1 kJmol-1 with electrostatics being the major term according to energy decomposition analysis.

High-resolution FTIR spectroscopy of 12C2HD3 in the 830–1110 cm−1 region: A study of the Coriolis and anharmonic interactions within the v3 = 1, v6 = 1 and v8 = 1 triad

The infrared spectrum of ethylene-d3 (12C2HD3) was measured between 830 and 1110 cm-1, covering the ν3, ν6 and ν8 bands, using a Fourier transform infrared (FTIR) spectrometer at an unapodized resolution of 0.0019 cm−1. The three upper vibrational states were found to mutually-interact through Coriolis and anharmonic resonances. A total of 2128 a- and b-type absorption lines of the ν3 band and 3107c-type lines of the ν8 band were assigned in this work. Although the ν6 band is relatively weak, 246 spectral lines were identified and included in the final fit for the rovibrational parameters of the upper vibrational states. Using a Hermitian Hamiltonian comprising Watson's-type rotational operators and off-diagonal interaction terms, three sets of rovibrational constants up to quartic terms were derived for the v3 = 1, v6 = 1 and v8 = 1 states together with thirteen interaction parameters, with a root-mean-square (rms) deviation of the fit = 0.00059 cm−1. The band centres of the ν3, ν6 and ν8 bands were determined to be 1044.260675 ± 0.000025 cm−1, 998.60182 ± 0.00060 cm−1 and 918.732573 ± 0.000019 cm−1 respectively. A set of ground state rovibrational constants of 12C2HD3 up to five quartic constants was also derived with improved precision from a simultaneous fit of 782 ground state combination differences (GSCDs) from a-type infrared transitions of the ν3 band and 1422 GSCDs from the c-type ν8 band from the present analysis, together with 377 GSCDs from the previous work on the 2ν8 band. The rms deviation of the GSCD fit was 0.00039 cm-1. The experimental spectroscopic parameters compare favourably with the quantum-chemically calculated values at the MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory.

Superstatistics of Schrödinger equation with pseudo-harmonic potential in external magnetic and Aharanov-Bohm fields

In this work, the thermodynamic properties of pseudo-harmonic potential in the presence of external magnetic and Aharanov-Bohm fields are investigated. The effective Boltzmann factor in the superstatistics formalism was used to obtain the thermodynamic properties such as Helmholtz free energy, Internal energy, entropy and specific heat capacity of the system. In addition, the thermal properties of some selected diatomic molecules of N2,Cl2,I2 and CH using their experimental spectroscopic parameters and the effect of varying the deformation parameter of q=0,0.3,0.7 were duly examined.

Theoretical studies for the infrared spectra of Ar–CO2 complex: Fundamental and combination bands

Two potential energy surfaces (PESs) were constructed for the ground and excited states of Ar–CO2 complex at the rigid rotor approximation. Besides the notable T-shape structure, two equivalent linear structures were also found on the PES for the first time. Based on the PESs of ground and excited states, the bound state calculations were performed to determine the rotational energy levels for the ground and excited states. In combination of the experimental spectroscopic parameters of ground state and the differences of rotational energy levels, we give a theoretical prediction of infrared spectra including one fundamental band and two combination bands for two isotopomers Ar–12C16O2 and Ar–12C18O2 in the ν3 region of CO2 monomer. The predicted transition frequencies and spectroscopic parameters of excited states are in excellent agreement with the available experimental data, and these results can also be used as a guide to perform the further investigation for the infrared spectra of combination bands experimentally.

Diving for Accurate Structures in the Ocean of Molecular Systems with the Help of Spectroscopy and Quantum Chemistry.

The prediction and interpretation of structural properties are the starting points for a deep understanding of thermochemistry, kinetics, and spectroscopic signatures of molecular systems. To give an example, detailed knowledge of the conformational behavior of the main building blocks of biomolecules in the gas phase (i.e., without the perturbing effect of the environment) is a mandatory prerequisite toward the understanding of the role played by different interactions in determining the biological activity in terms of structure-activity relationships. The first step to take is an unambiguous definition of molecular structure. We address the so-called Born-Oppenheimer equilibrium structure, which is defined in a rigorous manner and isotopically independent, and the target accuracy. For the latter, we aim at so-called "spectroscopic" accuracy, which implies uncertainties of a few milliangstroms for bond lengths and smaller than a tenth of degree for angles. If on one side the continuous enhancements of the experimental techniques give access to new and unprecedented spectroscopic determinations, on the other side they require increasing efforts for an unbiased interpretation and analysis. Among the pieces of information, accurate molecular structures play a particularly important role. Indeed, there is a strong relationship between the experimental outcome and the electronic structure of the system. Spectroscopic techniques, in particular those exploited in the gas phase, are therefore accurate and reliable sources for structural information. However, it is seldom straightforward to derive molecular structures directly from the experimental information. Indeed, even in the favorable case of investigations in the gas phase, vibrational effects are always present, and disentangling their contributions requires collection of information for all vibrational modes, a nearly impossible task. To overcome these limitations, joint theory-spectroscopy strategies can be identified, which are referred to as "top-down" and "bottom-up". The first approach, denoted as the semiexperimental approach, relies on extracting from experimental outcomes the equilibrium structure by using quantum-chemical computations to recover vibrational effects. The bottom-up approach consists in verifying the computed equilibrium geometry by means of a comparison between calculated and experimental spectroscopic parameters that probe structural characteristics. In this contribution, we try to review the most important challenges in accurate molecular structure determinations, with particular emphasis on the "solution" provided by a joint theoretical-experimental approach and on the current state of the art. Starting from the illustration of different strategies, we proceed by addressing the increasing complexity in the derivation of equilibrium geometries: we start from the construction of a database of accurate structures, we then face the problem of extending the dimension of the systems amenable to accurate structural determinations, and finally we move to the challenge of understanding the nature of intermolecular interactions.

An accurate prediction of the infrared spectra for Rg–CS2 (Rg = He, Ne, Ar) complexes in the ν1 + ν3 region of CS2 monomer

We constructed three potential energy surfaces (PESs) for the ground and excited states of each complex including He–CS2, Ne–CS2, and Ar–CS2, respectively. Based on these PESs, the bound state calculations were performed to determine the rotational levels of the ground and excited states. Combining the experimental spectroscopic parameters of ground state and the rotational level differences between the ground and excited states, we accurately predicted the infrared spectra in the ν1 and ν1 + ν3 regions of CS2 monomer. The determined spectroscopic parameters and transition frequencies are in excellent agreement with the available experimental data.

Redox Properties of Transition-Metal/Organic Chromophore Arrays: Interplay Between Metal- and Chromophore-Centered Electron-Transfer Processes

A large number of ferrocene-containing BODIPYs, azaBODIPYs, and BOPHYs along with several examples of non-innocent transition-metal aza-dipyrromethenes have been prepared and characterized by UV-Vis-NIR, NMR, HRMS, and X-ray crystallography. The redox properties of all target compounds were investigated by electrochemical and spectroelectrochemical methods. The experimental electronic, spectroscopic, and geometric parameters of the organometallic BODIPYs, azaBODIPYs, and BOPHYs as well as transition-metal aza-dipyrromethenes were correlated with DFT and TDDFT calculations.

Analytic functions for potential energy curves, dipole moments, and transition dipole moments of LiRb molecule

The analytic potential energy functions (APEFs) of the X1Σ+, 21Σ+, a3Σ+, and 23Σ+ states of the LiRb molecule are obtained using Morse long-range potential energy function with damping function and nonlinear least-squares method. These calculations were based on the potential energy curves (PECs) calculated using the multi-reference configuration interaction (MRCI) method. The reliability of the APEFs is confirmed using the curves of their first and second derivatives. By using the obtained APEFs, the rotational and vibrational energy levels of the states are determined by solving the Schrödinger equation of nuclear movement. The spectroscopic parameters, which are deduced using Dunham expansion, and the obtained rotational and vibrational levels are compared with the reported theoretical and experimental values. The correlation effect of the electrons of the inner shell remarkably improves the results compared with the experimental spectroscopic parameters. For the first time, the APEFs for the dipole moments and transition dipole moments of the states have been determined based on the curves obtained from the MRCI calculations.

Spectroscopic and calorimetric studies of interaction of methimazole with human serum albumin

The interaction of the anti-thyroid drug, 2-mercapto 1-methylimidazole (methimazole) with human serum albumin (HSA) has been examined by fluorescence and isothermal titration calorimetry (ITC) techniques. Fluorescence results indicate that in case of HSA–drug complex the quenching of fluorescence intensity is at 340nm. The methimazole has an ability to quench the intrinsic fluorescence of HSA tryptophan through a static quenching procedure. The binding constant has been determined using Stern–Volmer modified equation and energy transfer mechanisms of quenching are discussed. The ΔG°, ΔH°, and ΔS° values are also calculated by ITC measurements. The experimental spectroscopic and thermodynamic parameters have been used for understanding the binding mechanism of anti-thyroid drug with HSA.

Combination of EPR Measurements and DFT Calculations To Study Nitrate Impurities in the Carbonated Nanohydroxyapatite

We demonstrate the application of the combined experimental-computational approach for studying the anionic impurities in hydroxyapatite (HAp). Influence of the carbonation level (x) on the concentration of the NO3(2-) radicals in the HAp nanocrystals of Ca10-xNax(PO4)6-x(CO3)x(OH)2 with x in the range 0 < x < 2 and average sizes of 30 nm is investigated by different analytical methods including electron paramagnetic resonance (EPR). Stable NO3(2-) radicals are formed under X-ray irradiation of nano-HAp samples from NO3(-) ions incorporated in trace amounts during the wet synthesis process. Density functional theory (DFT) based calculations show energetic preference for the PO4 group substitution by NO3(-) ions. Comparison of the calculated and experimental spectroscopic parameters (g and hyperfine tensors) reveals that EPR detects the NO3(2-) radicals located in the positions of the PO4 group only. It is shown that with the increase in x, the carbonate ions substitute the NO3(2-)/NO3(-) ions. DFT calculations confirm that carbonate incorporation in HAp structure is energetically more favorable than the formation of the nitrate defect.

ChemInform Abstract: Computational Modelling of Oxygenation Processes in Enzymes and Biomimetic Model Complexes

AbstractReview: 108 refs.

Computational modelling of oxygenation processes in enzymes and biomimetic model complexes

With computational resources becoming more efficient and more powerful and at the same time cheaper, computational methods have become more and more popular for studies on biochemical and biomimetic systems. Although large efforts from the scientific community have gone into exploring the possibilities of computational methods for studies on large biochemical systems, such studies are not without pitfalls and often cannot be routinely done but require expert execution. In this review we summarize and highlight advances in computational methodology and its application to enzymatic and biomimetic model complexes. In particular, we emphasize on topical and state-of-the-art methodologies that are able to either reproduce experimental findings, e.g., spectroscopic parameters and rate constants, accurately or make predictions of short-lived intermediates and fast reaction processes in nature. Moreover, we give examples of processes where certain computational methods dramatically fail.

Theoretical studies of the CO2–N2O van der Waals complex: Ab initio potential energy surface, intermolecular vibrations, and rotational transition frequencies

Theoretical studies of the potential energy surface and bound states were performed for the CO(2)-N(2)O van der Waals complex. A four-dimensional intermolecular potential energy surface (PES) was constructed from 11,466 ab initio data points which were calculated at the coupled-cluster single double (triple) level with aug-cc-pVTZ basis set supplemented with bond functions. Three co-planar local minima were found on this surface. They correspond to two equivalent isomers with a slipped parallel structure in which the O atom in N(2)O is near the C atom in CO(2) and a T-shaped isomer in which the terminal N atom in N(2)O is closest to the C atom in CO(2). The two slipped parallel isomers are energetically more stable than the T-shaped isomer by 178 cm(-1). Four fundamental vibrational excited states for the slipped parallel isomers and two fundamental vibrational excited states (torsion and disrotation) for the T-shaped isomer were assigned via bound states calculations based on this PES. The theoretical vibrational frequencies are in good agreement with the available experimental values for the slipped parallel isomers. Rotational excitations (J = 0-6) for the ground vibrational state of the slipped parallel structure were calculated and the accuracy of the PES in the vicinity of minima is validated by the good agreement between the theoretical and experimental transition frequencies and spectroscopic parameters.

Numerical Modeling of Holmium-Doped Fluoride Fiber Lasers

We combine all the known experimental demonstrations and spectroscopic parameters into a numerical model of the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Ho}^{3+}$</tex></formula> -doped fluoride glass fiber laser system. Core-pumped and cladding-pumped arrangements were simulated for all the population-bottlenecking mitigation schemes that have been tested, and good agreement between the model and the previously reported experimental results was achieved in most but not in all cases. In a similar way to <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm Er}^{3+}$</tex></formula> -doped fluoride glass fiber lasers, we found that the best match with measurements required scaled-down rate parameters for the energy transfer processes that operate in moderate to highly concentrated systems. The model isolated the dominant processes affecting the performance of each of the bottlenecking mitigation schemes and pump arrangements. It was established that pump excited-state absorption is the main factor affecting the performance of the core-pumped demonstrations of the laser, while energy transfer between rare earth ions is the main factor controlling the performance in cladding-pumped systems.

Application of DFT methods to the study of the coordination environment of the VO2+ ion in V proteins.

Density functional theory (DFT) methods were used to simulate the environment of vanadium in several V proteins, such as vanadyl-substituted carboxypeptidase (sites A and B), vanadyl-substituted chloroplast F(1)-ATPase (CF(1); site 3), the reduced inactive form of vanadium bromoperoxidase (VBrPO; low- and high-pH sites), and vanadyl-substituted imidazole glycerol phosphate dehydratase (IGPD; sites α, β, and γ). Structural, electron paramagnetic resonance, and electron spin echo envelope modulation parameters were calculated and compared with the experimental values. All the simulations were performed in water within the framework of the polarizable continuum model. The angular dependence of [Formula: see text] and [Formula: see text] on the dihedral angle θ between the V=O and N-C bonds and on the angle φ between the V=O and V-N bonds, where N is the coordinated aromatic nitrogen atom, was also found. From the results it emerges that it is possible to model the active site of a vanadium protein through DFT methods and determine its structure through the comparison between the calculated and experimental spectroscopic parameters. The calculations confirm that the donor sets of sites B and A of vanadyl-substituted carboxypeptidase are [[Formula: see text], H(2)O, H(2)O, H(2)O] and [N(His)(||), N(His)(⊥), [Formula: see text], H(2)O], and that the donor set of site 3 of CF(1)-ATPase is [[Formula: see text], OH(Thr), H(2)O, H(2)O, [Formula: see text]]. For VBrPO, the coordination modes [N(His)(||), N(His)(∠), OH(Ser), H(2)O, H(2)O(ax)] for the low-pH site and [N(His)(||), N(His)(∠), OH(Ser), OH(-), H(2)O(ax)] or [N(His)(||), N(His)(∠), [Formula: see text], H(2)O] for the high-pH site, with an imidazole ring of histidine strongly displaced from the equatorial plane, can be proposed. Finally, for sites α, β, and γ of IGPD, the subsequent deprotonation of one, two, and three imidazole rings of histidine and the participation of a carboxylate group of a glutamate residue ([N(His)(||), [Formula: see text], H(2)O, H(2)O], [N(His)(||), N(His)(||), [Formula: see text], H(2)O], and [N(His)(||), N(His)(||), [Formula: see text], OH(-), [Formula: see text]], respectively) seems to be the most plausible hypothesis.

MRCI study of potential energy curves, spectroscopic and molecular properties of the CO + cation

The potential energy curves (PECs) of nine low-lying electronic states (X 2Σ +, A 2Π, B 2Σ +, C 2Δ, D 2Π, a 4Σ +, 1 4Δ, b 4Π and 1 4Σ −) of the CO + cation have been studied using an ab initio quantum chemical method. The calculations have been performed employing the complete active space self-consistent field (CASSCF) method followed by the valence internally contracted multireference configuration interaction (MRCI) approach in combination with a correlation-consistent aug-cc-pV5Z basis set. To improve the quality of the PECs, core–valence correlation and relativistic corrections are included. Relativistic corrections are included using the third-order Douglas–Kroll Hamiltonian approximation. Core–valence correlation corrections are included using a cc-pCVQZ basis set. Relativistic corrections are included at the level of the cc-pV5Z basis set. In order to obtain more reliable results, the PECs determined by the MRCI calculations are also corrected for size-extensivity errors by means of the Davidson modification (MRCI+Q). Analyses show that the effects on the spectroscopic parameters by the core–valence correlation correction, relativistic correction and Davidson modification are obvious, whereas the effect on the spectroscopic parameters by the nonadiabatic correction can be neglected. For the X 2Σ +, A 2Π, B 2Σ + and C 2Δ electronic states, six main isotopologues ( 12C 16O +, 12C 17O +, 12C 18O +, 13C 16O +, 13C 17O + and 13C 18O +) have been studied, since their experimental spectroscopic parameters and molecular constants are relatively abundant. For the D 2Π, a 4Σ +, 1 4Δ, 1 4Σ − and b 4Π electronic states, just the most naturally abundant isotopologue, 12C 16O +, is investigated. These results have been compared in detail with those reported in the literature. Excellent agreement has been found between the present results and the experimentally determined ones. The molecular constants of the C 2Δ and the spectroscopic parameters of the D 2Π, a 4Σ +, 1 4Δ, 1 4Σ − and b 4Π electronic states determined by the MRCI+Q/aug-cc-pV5Z+CV+DK calculations are expected to be reliable predicted results.

The Unusual Electronic Structure of Dinitrosyl Iron Complexes

Dinitrosyl iron complexes (DNICs) are implicated in the degradation and reassembly chemistry of iron-sulfur clusters; however, their electronic structure is not well understood. Here, experimentally validated electronic structures of a {Fe(NO)(2)}(9) species and its one-electron reduced form, {Fe(NO)(2)}(10), were reached through a detailed analysis of the Kohn-Sham density functional solutions that successfully reproduce the experimental structures and spectroscopic parameters. The {Fe(NO)(2)}(9) unit is best rationalized by a resonance hybrid consisting of a HS ferric center (S(Fe) = 5/2) antiferromagnetically coupled to two NO(-) ligands (S((NO)(2)) = 2) and a HS ferrous ion (S(Fe) = 2) coupled to an overall (4)(NO)(2)(-) ligand (S((NO)(2)) = 3/2) in an antiferromagnetic fashion. The {Fe(NO)(2)}(10) species is best interpreted as a HS ferrous center (S(Fe) = 2) that is antiferromagnetically coupled to two triplet NO(-) ligands (S((NO)(2)) = 2). A salient feature of this electronic structure description is the very covalent bonding involving the iron center and the two NO ligands. As a result, a "one-above-four" ligand field splitting pattern is identified in DNICs, in which four of the five Fe-3d orbitals are strongly pi-bonding MOs with respect to the Fe-NO interaction while the last Fe 3d-based orbital remains essentially nonbonding. The latter acts as the electron acceptor orbital for the one-electron reduction of the {Fe(NO)(2)}(9) species. This unusual ligand field splitting pattern may have mechanistic implications for the degradation and reassembly chemistry of iron-sulfur clusters involving DNICs.

A novel analytic potential function applied to neutral diatomic molecules and charged lons

In this paper, a new method on constructing analytical potential energy functions is pre-sented, and from this a analytical potential en-ergy function applied to both neutral diatomic molecules and charged diatomic molecular ions is obtained. This potential energy function in-cludes three dimensionless undetermined pa-rameters which can be determined uniquely by solving linear equations with the experimental spectroscopic parameters of molecules. The solutions of the dimensionless undetermined parameters are real numbers rather than com-plex numbers, this ensures that the analytical potential energy function has extensive uni-versality. Finally, the potential energy function is examined with four kinds of diatomic molecules or ions—homonuclear neutral diatomic mole-cule , and , homonuclear charged diatomic molecular ion , and , heter-nuclear neutral diatomic Molecule , and , heternuclear ch- arged diatomic Molecular ion , and ,as a conseque- nce, good results are obtained.