Vibrational Band Positions Research Articles

Studies on the Authorship of Albumen Vintage Photographs: A Combined Experimental and Chemometric Approach.

The differences in albumen photographs from vintage photographic studios were identified by energy-dispersive X-ray fluorescence spectroscopy and Fourier transform infrared spectroscopy. The results inspired the concept of finding common features characteristic of a given photographic studio. The obtained measurement data (i.e., positions of vibrational bands for characteristic groups of albumen and the mass contents of chosen elements) were analyzed chemometrically by employing the Principal Component Analysis (PCA). The PCA technique allowed us to reduce the number of relevant experimental parameters characterizing the unique features of the photographic objects. The two major components were able to distinguish the photographic objects in terms of their authorship and the time to produce a photograph. The method developed was examined for a selected group of photographs consisting of albumen prints from three Polish photographic ateliers. To validate ED-XRF measurements and, consequently, the chemometric findings, reference albumen photo samples were designed and prepared. The empirical functional relationships between the content of photochemically reduced silver particles on the photographic paper and several physicochemical factors, including time of exposure to UV light, AgNO3 concentration in a fixed bath, and concentrations of other additives, were proposed. These results can be used for the prediction of the experimental conditions under which the investigated photographs were developed.

Metal nanoparticles supported on a nonconductive oxide undergo pH-dependent spontaneous polarization.

Electrochemical polarization, which often plays a critical role in driving chemical reactions at solid-liquid interfaces, can arise spontaneously through the exchange of ions and/or electrons across the interface. However, the extent to which such spontaneous polarization prevails at nonconductive interfaces remains unclear because such materials preclude measuring and controlling the degree of interfacial polarization via standard (i.e., wired) potentiometric methods. Herein, we circumvent the limitations of wired potentiometry by applying infrared and ambient pressure X-ray photoelectron spectroscopies (AP-XPS) to probe the electrochemical potential of nonconductive interfaces as a function of solution composition. As a model class of macroscopically nonconductive interfaces, we specifically probe the degree of spontaneous polarization of ZrO2-supported Pt and Au nanoparticles immersed in aqueous solutions of varying pH. Shifts in the Pt-adsorbed CO vibrational band position evince electrochemical polarization of the Pt/ZrO2-water interface with changing pH, and AP-XPS reveals quasi-Nernstian shifts of the electrochemical potential of Pt and Au with pH in the presence of H2. These results indicate that spontaneous proton transfer via equilibrated H+/H2 interconversion spontaneously polarizes metal nanoparticles even when supported on a nonconductive host. Consequently, these findings indicate that solution composition (i.e., pH) can be an effective handle for tuning interfacial electrical polarization and potential at nonconductive interfaces.

Probing computational methodologies in predicting mid-infrared spectra for large polycyclic aromatic hydrocarbons

ABSTRACT We extend the prediction of vibrational spectra to large sized polycyclic aromatic hydrocarbon (PAH) molecules comprising up to ∼1500 carbon atoms by evaluating the efficiency of several computational chemistry methodologies. We employ classical mechanics methods (Amber and Gaff) with improved atomic point charges, semi-empirical (PM3, and density functional tight binding), and density functional theory (B3LYP) and conduct global optimizations and frequency calculations in order to investigate the impact of PAH size on the vibrational band positions. We primarily focus on the following mid-infrared emission bands 3.3, 6.2, 7.7, 8.6, 11.3, 12.7, and 17.0 μm. We developed a general Frequency Scaling Function ($\mathcal {FSF}$) to shift the bands and to provide a systematic comparison versus the three methods for each PAH. We first validate this procedure on IR scaled spectra from the NASA Ames PAH Database, and extend it to new large PAHs. We show that when the $\mathcal {FSF}$ is applied to the Amber and Gaff IR spectra, an agreement between the normal mode peak positions with those inferred from the B3LYP/4-31G model chemistry is achieved. As calculations become time intensive for large sized molecules Nc > 450, this proposed methodology has advantages. The $\mathcal {FSF}$ has enabled extending the investigations to large PAHs where we clearly see the emergence of the 17.0 μm feature, and the weakening of the 3.3 μm one. We finally investigate the trends in the 3.3 μm/17.0 μm PAH band ratio as a function of PAH size and its response following the exposure to fields of varying radiation intensities.

Searching for Monomeric Nickel Tetrafluoride: Unravelling Infrared Matrix Isolation Spectra of Higher Nickel Fluorides

AbstractBinary transition metal fluorides are textbook examples combining complex electronic features with most fundamental molecular structures. High‐valent nickel fluorides are among the strongest known fluorinating and oxidizing agents, but there is a lack of experimental structural and spectroscopic investigations on molecular NiF3 or NiF4. Apart from their demanding synthesis, also their quantum‐chemical description is difficult due to their open shell nature and low‐lying excited electronic states. Distorted tetrahedral NiF4 (D2d) and trigonal planar NiF3 (D3h) molecules were produced by thermal evaporation and laser ablation of nickel atoms in a fluorine/noble gas mixture and spectroscopically identified by a joint matrix‐isolation and quantum‐chemical study. Their vibrational band positions provide detailed insights into their molecular structures.

Searching for Monomeric Nickel Tetrafluoride: Unravelling Infrared Matrix Isolation Spectra of Higher Nickel Fluorides.

Binary transition metal fluorides are textbook examples combining complex electronic features with most fundamental molecular structures. High‐valent nickel fluorides are among the strongest known fluorinating and oxidizing agents, but there is a lack of experimental structural and spectroscopic investigations on molecular NiF3 or NiF4. Apart from their demanding synthesis, also their quantum‐chemical description is difficult due to their open shell nature and low‐lying excited electronic states. Distorted tetrahedral NiF4 (D 2d) and trigonal planar NiF3 (D 3h) molecules were produced by thermal evaporation and laser ablation of nickel atoms in a fluorine/noble gas mixture and spectroscopically identified by a joint matrix‐isolation and quantum‐chemical study. Their vibrational band positions provide detailed insights into their molecular structures.

Laboratory gas-phase vibrational spectra of [C3H3]+ isomers and isotopologues by IRPD spectroscopy

Gas phase vibrational spectra of [C3H3]+ isomers and their fully deuterated isotopologues measured in a cryogenic 22-pole ion trap are presented. The widely tunable free electron laser for infrared experiments, FELIX, was employed to cover the frequency range 500–2400 cm−1, complemented with an OPO/OPA system covering 2800–3400 cm−1. Spectral assignments for both the linear and cyclic isomeric form (H2C3H+ and c-C3H3+, respectively) are made based on various high-level computational studies. The effect of ion source conditions and different precursors (allene and propargyl chloride) for the preferential production of a specific isomer is discussed. The perturbation of the vibrational band position due to complexation with neon in the recorded infrared-predissociation (IRPD) spectra are also reported in this study.

Determination of vibrational band positions in the E-hook of β-tubulin.

Raman spectral characterization of the β-TUBB2A E-hook hexapeptide, EGEDEA, is determined through experimental analysis combined with full geometry optimizations and corresponding harmonic vibrational frequency computations employing DFT methods. The hexapeptide is first broken down into di- and tetrapeptide fragments which are analyzed both quantum chemically and experimentally, and then combined to achieve an energetic minimum of the large EGEDEA hexapeptide. The Raman spectral characterization of EGEDEA band positions are then verified via the literature and comparison to the small fragment's similarly located band positions. The approach employed provides further evidence for the use of fragments as a helpful tool in characterization of the vibrational band positions of large peptides. STATEMENT OF SIGNIFICANCE: To investigate β-TUBB2A E-hook hexapeptide, a unique approach is employed whereby the hexapeptide is broken into fragments, EG, ED, EA, EGED, and EDEA and analyzed via experimental Raman spectroscopy of the crystalline solids. The experimentally observed vibrational band positions are compared to those computed using and scaled from DFT methods and Pople's 6-311+G(2df,2pd) basis set. The reported vibrational band positions are also confirmed by previously reported bands of similar peptides in the literature. This methodology facilitates differentiation between the behaviors of various side chains and their influence on the structure of the hexapeptide, providing insight into not only the nature of the peptide but also defining regions for potential protein and cytoplasmic interactions, without requiring excessive computing resources or overly-sensitive experimental methods.

Structural, optical, mechanical, and electronic properties of Cr-doped alumina

Cr-doped α-Al2O3 samples (Al2−xCrxO3, 0 ≤ x ≤ 0.25; step 0.05) were synthesized by citrate-precursor autocombustion method. The lattice parameters, bond distortion index, crystallite size, and lattice microstrain of the developed system were investigated using Rietveld profile method. The porous nature of the formed samples was elucidated by a scanning electron microscope. The effect of doping on the vibrational band positions was examined using Fourier-transform infrared technique. The photoluminescence emission showed that a red color was mainly exhibited by all samples, while that with x = 0.05 showed the highest intensity. Other colors appear with a small intensity for higher Cr-doped samples. The electronic, optical, and mechanical stability properties of undoped and doped samples were investigated using density-functional theory calculation.

Theoretical Vibrational Spectra of Reaction Intermediates in the Active Site of Guanosine Triphosphate Binding Proteins

Calculations of the structures and energies of intermediates of the enzymatic hydrolysis of guanosine triphosphate, performed by means of quantum mechanics and molecular mechanics (QM/MM), suggest a mechanism for chemical transformations of reaction particles in an active site that assumes an amide-imide tautomerism of the side chain of glutamine residue. Positions of vibrational bands and a corresponding band shift upon isotopic substitution 14N → 15N in the side chain of glutamine residue in the active site are predicted for experimental verification of the given mechanism via IR spectroscopy.

Structural and optical properties of Sm3+-doped borate glasses for luminescent applications

In this work, most interesting optical investigations are carried out with the glass composition (20 − x) CdCO3 + 15 Li2CO3 + 15 Na2CO3 + 50 H3BO3 + xSm2O3 (where x = 0.1, 0.5, 1.0, 3.0, 4.0 and 5.0 mol%) prepared with conservative melt-quenching technique. DSC verifies the annealing temperature and thermal stability of the prepared glass. X-ray diffraction technique is employed to inspect the amorphous structure of the glasses. FTIR technique helps to view the vibrational band positions of the host material. For optical studies, optical absorption and emission measurements are used. From the absorption spectra, Judd–Ofelt (JO) parameters (Ω2, Ω4, Ω6), rms value of oscillator strength ($$\delta_{rms}$$), nephelauxetic parameter ($$\bar{\beta }$$), bonding parameter ($$\delta$$) and optical band gaps are evaluated. Radiative properties such as radiative transition probabilities (AT), branching ratios (βcal, βexp) and stimulated emission cross section (σemi) are calculated using JO theory. The higher stimulated emission cross section (14.39 × 10−22 cm2), optical gain (36.69 × 10−25 cm2 s) indicate that 1.0 mol% of Sm3+-doped borate glass would be a potential gain medium for solid state laser application at 603 nm. Color coordinates of the glasses located in the reddish-orange region could be useful for white light-emitting application.

Aggregation of lactic acid in cold rare-gas matrices and the link to solution: a matrix isolation-vibrational circular dichroism study.

The matrix isolation (MI) technique has been utilized with vibrational circular dichroism (VCD) spectroscopy to obtain MI-VCD spectra of lactic acid (LA) in cold argon matrices, in addition to their MI-IR spectra. The experiments have been done at three different deposition temperatures (10 K, 16 K and 24 K) under different Ar flow rates so that different degrees of LA self-aggregation occur. The structural and spectral investigations of the LA monomer and the larger (LA)2,3,4 aggregates have been undertaken at three levels of theory (B3LYP/6-311++G(2d,p), B3LYP-D3BJ/6-311++G(2d,p) and B3LYP-D3BJ/def2-TZVPD) to evaluate the effects of dispersion correction and basis sets on optimized structures, relative conformer energies, and IR/VCD spectral features. Interestingly, the relative conformer energies vary considerably with and without dispersion correction, especially when the molecule gets larger and when it is placed in solution. Such uncertainties in the relative energies and in the vibrational band positions and IR/VCD intensities highlight the challenges in interpreting experimental spectroscopic data, especially those obtained in solution. With the narrow MI-IR band width and highly characteristic MI-VCD spectral features and the trend observed at three temperatures, we have been able to correlate the spectral features confidently to those of the LA monomer and the larger (LA)2,3,4 aggregates, with the aid of theoretical modeling. Finally, by noting the similarity of MI-IR and especially MI-VCD features obtained at 24 K with those of the 0.2 M solution, and with the aid of spectral simulation at the B3LYP-D3BJ/def2-TZVPD level, a composition of LA aggregates dominated by the LA tetramer and trimer has been identified. This conclusion differs from the previous reports where the LA dimer was identified as the main species at even higher concentration in CDCl3. The present work showcases the power of MI-VCD spectroscopy in aiding solution spectral assignment and in providing insight into the complex self-aggregation behavior of LA in solution.

Observation of anomalous site occupancy in Ni-Co-Cu-Cr ferrite system synthesized by sol-gel method

Anomalous variation in cation distribution in chromium doped Ni-Co-Cu-Cr ferrites synthesized by sol-gel method has been observed the formation of spinel structure and explained with the help of DTA/TG and X-ray diffraction analysis. Error estimated between theoretical and calculated lattice parameter based on proposed cation distribution is found be in range of 0.0014% to 0.00005%, which confirms the cation distribution predicted for the present samples. In this present work, it appears that most of the cobalt and 50% of nickel ions are observed to occupy A-sites instead of B-sites of spinel lattice, which is a drastic deviation from the reports published till date. The g-value have been found to be lower for x = 0.02 concentration as observed from ESR analysis. Fourier transform infrared spectroscopic techniques (FTIR) show no variation in peak position of vibrational bands, indicates the uniform bond length in the spinel ferrite, even for different concentration of chromium. This is further confirmed by the bond length calculation using empirical formulas and experimental lattice parameters, showing least error for shared and unshared ion for tetrahedral or octahedral sites.

Infrared absorption spectra of N(CxF2x+1)3, x = 2–5 perfluoroamines

Infrared absorption spectra of the perfluoroamines (N(C2F5)3, N(C3F7)3, N(C4F9)3, and N(C5F11)3) were measured over the 500–4000 cm−1 spectral region at 294 K using Fourier transform infrared (FTIR) spectroscopy at 1 cm−1 resolution. Spectral measurements were performed using static measurements of dilute perfluoroamines mixtures and by infusion of the pure compound into a calibrated gas flow. The perfluoroamines absorb strongly in the “atmospheric window” with integrated band strengths (10−17 cm2 molecule−1 cm−1) between 570 and 1500 cm−1 of 59.9, 74.9, 88.9, and 98.7 for N(C2F5)3, N(C3F7)3, N(C4F9)3, and N(C5F11)3, respectively. Radiative efficiencies (RE) for the perfluoroamines were estimated to be 0.61, 0.75, 0.87, and 0.95 W m−2 ppb−1 for atmospherically well-mixed conditions and including a +10% stratospheric temperature correction for N(C2F5)3, N(C3F7)3, N(C4F9)3, and N(C5F11)3, respectively. Theoretical calculations of the perfluoroamines were performed at the B97-1/6-311++G(2df,2p) level of theory and optimized perfluoroamine geometries, vibrational band positions, and band strengths are reported. The theoretically calculated infrared spectra are in good agreement with the experimental spectra, while comparison of individual bands was not attempted due to the significant overlap of vibrational bands in the experimental spectra.

Spectroscopy of the low-frequency vibrational modes of [formula omitted] isotopologues

The low-frequency stretching and bending vibrations of the isotopologues CH2D+,CD2H+ and CD3+ have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions CDmHn++H2→hνCDm-1Hn+1++HD have been applied for these species. As this scheme is not applicable to CH3+, the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting CH3+-He spectrum, broad features are observed below 1000 cm-1 possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations.

Laboratory Gas-phase Infrared Spectra of Two Astronomically Relevant PAH Cations: Diindenoperylene, and Dicoronylene,

Abstract The first gas-phase infrared spectra of two isolated astronomically relevant and large polycyclic aromatic hydrocarbon (PAH) cations—diindenoperylene (DIP) and dicoronylene (DC)—in the 530–1800 cm−1 (18.9−5.6 μm) range—are presented. Vibrational band positions are determined for comparison to the aromatic infrared bands. The spectra are obtained via infrared multiphoton dissociation spectroscopy of ions stored in a quadrupole ion trap using the intense and tunable radiation of the free electron laser for infrared experiments (FELIX). DIP+ shows its main absorption peaks at 737 (13.57), 800 (12.50), 1001 (9.99), 1070 (9.35), 1115 (8.97), 1152 (8.68), 1278 (7.83), 1420 (7.04), and 1550 (6.45) cm−1(μm), in good agreement with density functional theory (DFT) calculations that are uniformly scaled to take anharmonicities into account. DC+ has its main absorption peaks at 853 (11.72), 876 (11.42), 1032 (9.69), 1168 (8.56), 1300 (7.69), 1427 (7.01), and 1566 (6.39) cm−1(μm), which also agree well with the scaled DFT results presented here. The DIP+ and DC+ spectra are compared with the prominent infrared features observed toward NGC 7023. This results both in matches and clear deviations. Moreover, in the 11.0–14.0 μm region, specific bands can be linked to CH out-of-plane (oop) bending modes of different CH edge structures in large PAHs. The molecular origin of these findings and their astronomical relevance are discussed.

Impact of crystalline and amorphous iron- and aluminum hydroxides on mechanisms of phosphate adsorption and desorption

Fourier-transform infrared (FT-IR) spectroscopic experiments were carried out during phosphate adsorption on highly crystalline gibbsite, poorly crystalline 2-line-ferrihydrite and amorphous iron–aluminum–hydroxide mixtures in the molar ratio 1:0, 10:1, 5:1, 1:1, 1:5, 1:10 and 0:1. The OH stretching vibrational bands were utilized to analyze changes in structural and surface OH groups during adsorption, because the position of characteristic PO vibrational bands can shift depending on reaction conditions, pH or adsorbed phosphate content. Adsorption and desorption kinetics were studied at pH6 and different initial phosphate concentrations to achieve varying phosphate coverage on the mineral surfaces. For gibbsite the formation of AlHPO4 and Al2HPO4 can be assumed, while for ferrihydrite, a FeHPO4 or Fe2PO4 complex and the precipitation of FePO4 with longer equilibration time were proposed. Fe2HPO4 or a Fe2PO4 surface complex was deduced for Fe-hydroxides, an AlH2PO4 surface complex was identified for Al-hydroxide, and both displayed either hydrogen bonds to neighboring hydroxyl groups or hydrogen bonds to outer-sphere complexes. Fe:Al-hydroxide mixtures with high Al ratios showed a low phosphate desorption rate, while ferrihydrite and the Fe:Al-hydroxide mixtures with high Fe ratios had almost negligible desorption rates. It was concluded that within the weakly associated amorphous FeO(OH) materials, FePO4 precipitated, which was bound by outer-sphere hydrogen bonds. With high Al ratios, desorption increased, which indicated weaker phosphate binding of both inner-sphere and outer-sphere complexes and hence, either no or minor quantities of precipitate. Ferrihydrite showed a more rigid structure and a lower extent of precipitation compared to amorphous Fe-hydroxide.

Near-infrared spectroscopy and anharmonic theory of the H2O+Ar1,2 cation complexes

Weakly bound complexes of the water radical cation with argon (H2O+Arn, n = 1,2) were generated by an electrical discharge/supersonic expansion and probed with mid- and near-infrared photodissociation spectroscopy in the 2050-4550 and 4850-7350 cm-1 regions. To elucidate these spectra, these complexes were studied computationally at the CCSD(T) level including anharmonicity with the VPT2 method. The comparison between experiment and predicted spectra demonstrates that the VPT2 method is adequate to capture most of the vibrational band positions and their intensities. In addition to the fundamentals, overtones of the symmetric and the asymmetric water stretches and their combination were detected. Additional bands were assigned to combinations of the overtone of the bound O-H stretch with multiple excitation levels of the intermolecular Ar-H stretch. H2O+Ar2 could not be dissociated in the higher frequency region (4850-7350 cm-1).

Infrared absorption spectra of linear (L2–L5) and cyclic (D3–D6) permethylsiloxanes

Absolute infrared absorption spectra of the linear (hexamethyldisiloxane ((CH3)3SiOSi(CH3)3, L2), octamethyltrisiloxane ([(CH3)3SiO]2Si(CH3)2, L3), decamethyltetrasiloxane ([(CH3)3SiO]2(Si(CH3)2OSi(CH3)2), L4), dodecamethylpentasiloxane ([(CH3)3SiO]2(Si(CH3)2OSi(CH3)2OSi(CH3)2), L5), and cyclic hexamethylcyclotrisiloxane ([Si(CH3)2O]3, D3), octamethylcyclotetrasiloxane ([Si(CH3)2O]4, D4), decamethylcyclopentasiloxane ([Si(CH3)2O]5, D5), and dodecamethylcyclohexasiloxane ([Si(CH3)2O]6, D6)) permethylsiloxanes were measured over the 600–4000 cm−1 spectral region at 294 K using Fourier transform infrared (FTIR) spectroscopy at 1 cm−1 resolution. Measurements were performed using manometrically prepared dilute permethylsiloxane mixtures in a He bath gas and infusion of the pure compound into a calibrated gas flow. Theoretical calculations at the B97-1/6-311++G(2df,2p) level of theory were performed and optimized permethylsiloxane geometries and vibrational band positions and strengths are reported. The theoretically calculated infrared spectra are compared with the experimental spectra and found to be in good agreement. The radiative efficiencies (RE) of the permethylsiloxanes were calculated and found to be extremely large in comparison with other atmospheric greenhouse gases, with values ranging from 0.55 to 2.02 W m−2 ppb−1 for a uniform atmospheric distribution, i.e., well-mixed scenario.

The effect of Li2O and LiF on structural properties of cobalt doped borate glasses

Two glassy (LiF–B2O3) and (Li2O–B2O3) systems containing different content of CoO dopants (0.05, 0.1, 0.15, 0.2wt%) were prepared. UV/Vis optical absorption of base glasses reveals a strong UV absorption bands attributed to unavoidable contaminated trace iron impurities. CoO-doped glasses show extra three visible bands due to both octahedral and tetrahedral Co2+ ions related to the little variation between energies of ligand field stabilization between the two coordination states. Fluoride containing glasses show limited variations in the spectral properties due to the different ligand strength of the anions (F− and O2−). FTIR spectra display characteristic modes of vibrations due to triangular and tetrahedral borate groups. It is assumed that LiF acts as Li2O in promoting the formation of tetrahedral (BO3F) units which possess the same wavenumber position for vibrations of (BO4) units in the range of 800–1200cm−1. CoO causes no distinct variations in number or position of characteristic IR vibrational bands due to their low dopant level (0.05–0.2%). A new suggested trial has been utilized to calculate the percent of four coordinated borons from both optical and FTIR spectra to give more insight on the role of CoO as dopant on these spectral properties and on the calculated parameters.

Sol-gel auto combustion synthesis, electrical and dielectric properties of Zn1−xCoxO (0.0 ≤ x ≤ 0.36) semiconductor nanoparticles

In the present work, Co2+ ion doped zinc oxide nanoparticles Zn1−xCoxO (x = 0.00, 0.06, 0.12, 0.18, 0.24, 0.30 and 0.36 mol) were synthesized by sol-gel auto combustion method. The effects of heavily doped Co2+ ion concentration on the structural, electrical and dielectric properties were studied. The prepared nanoparticles were characterized by X-ray diffraction technique (XRD), transmission electron microscopy (TEM), selected area diffraction pattern (SAED) and Fourier transform infrared spectroscopy (FT-IR). The X-ray diffraction analysis revealed the formation of single phase having hexagonal wurtzite structure along with secondary phase (Co3O4). TEM analysis clearly showed the small agglomeration and spherical shape of nanoparticles. SAED pattern also confirms the hexagonal wurtzite structure with single crystalline nature. FTIR analysis showed the vibrational frequency band position of Zn–O shifted to higher frequency band with Co2+ ion increasing host semiconductor nanoparticles. The temperature dependent (300–400 K) DC resistivity of samples was studied by the standard two probe method. DC electrical resistivity was found to increase with increasing Co2+ content in ZnO matrix. The dielectric properties of pure and Co2+ doped ZnO nanoparticles were studied as a function of frequency and composition using the LCR–Q meter. All the dielectric parameters show dispersion and decreases with increase in Co2+ content. The observed dielectric behavior is explained on the basis of Maxwell–Wagner model and Koops phenomenological theory.