Absolute Absorption Intensities Research Articles

A robust dipole moment of carbon monoxide (CO) is a permanent puzzle for both spectroscopic and ab initio studies

The asymptotically correct semi-empirical dipole moment function (DMF) for the ground X 1 Σ + state of the CO molecule was redetermined in an analytical form for the entire range of interatomic distances r ∈ [ 0 , + ∞ ] by a global least-squared fitting both experimental intensities and ab initio data. The region r ∈ [ 0.8 , 1.9 ] Å that is governed exclusively by the empirical data was broadened by adding experimental relative intensity ratios measured in the emission from high vibrational levels v. Absolute absorption intensities recently obtained for very high 7-0 overtone and accompanied sub-percent measurements for 3-0 band were also included in the fitting procedure. The present DMF reproduces a vast majority of the experimental intensities up to v ≤ 38 within accuracy of measurements, except ‘abnormally’ sensitive 5-0 band, and systematically overestimates the most previous ab initio and semi-empirical functions at r ≥ 1.5 Å . Possible reasons of the observed discrepancies are throughout discussed. The resulting DMF can be used, along with mass-invariant interatomic potential, to upgrade rovibrational line lists for any isotopologues of the CO molecule up to the dissociation threshold. The corresponding FORTRAN subroutine is provided.

Green route synthesis of silver nanoparticles using plants/ginger extracts with enhanced surface plasmon resonance and degradation of textile dye

Silver nanoparticles (AgNPs) of 10–20 nm sized were synthesized via eco-friendly and cost-effective green methods using ginger (Zingiber officinale) extract and exhibit an excellent crystalline structure. The AgNPs show absorption maximum at around 407 nm at an optimal pH of 10, hence exhibits a strong surface plasmon resonance (SPR), which arises when the interaction of free electron oscillation of AgNPs is in resonance with the frequency of light interacted. AgNPs growth could be controlled by changing environmental factors such as pH, temperature, reaction time and concentration. The development of AgNPs using ginger extract is much higher as compared to tulsi (Ocimum sanctum) and neem (Azadirachta indica), plant nectar (honey), pomegranate peel extracts and fructose. In the presence of catalyst AgNPs, the absolute absorption intensity (absorbance) of textile dye, methylene blue (MB) is reduced dramatically by sodium borohydride (NaBH4). The absorbance of MB diminished 99.9% and the solution became colorless (in 10 min). Thus, the hazardous dye is degraded faster by AgNPs than the metal oxides/NPs used so far. Note that most medicinal plant extracts used in the present study are quite helpful for several diseases, including coronavirus (Covid-19).

Optical Absorption Cross-Section of DNA Bases—Thymine and Guanine—in the Energy Region from 3.1 to 250 eV (5–400 nm)

(1) Background: Optical absorption cross-section—the absolute absorption intensity specific to each molecule—of nucleic acid bases enables us to estimate the reaction yields of DNA lesions induced by the exposure to not only photons but also ionizing radiations. However, it was unknown in the energy region exceeding ~10 eV (wavelength < ~120 nm). (2) Methods: Thin films of DNA bases—thymine and guanine—were prepared using a vacuum sublimation technique. Absorption spectra of these films were measured in the energy region from 3.1 to 250 eV (5–400 nm) at the synchrotron radiation facility UVSOR. (3) Results: The absorption spectra of both bases exhibited prominent absorption peaks around 20 eV and smaller peaks in the energy region below 10 eV. The determined optical oscillator strength distribution was verified to be reasonable based on the Thomas–Reiche–Kuhn oscillator strength sum rule. (4) Conclusion: Most of the oscillator strength distribution was positioned in the measured energy region, and therefore the absorption spectra significantly contributed to the quantitative study for the photo and radiation-chemical reactions of DNA.

Enhanced photoinduced catalytic activity of transition metal ions incorporated TiO2 nanoparticles for degradation of organic dye: Absorption and photoluminescence spectroscopy

Abstract Transition metal ions (Ag+, Cu2+, and Ni2+) doped and undoped TiO2 nanoparticles (NPs) were synthesized via cost effective sol-gel method with 1.0 wt% dopant concentration. The microstructure and chemical compositions of these NPs were examined using various techniques such as x-ray diffractometry, field emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared and absorption and photoluminescence (PL) spectroscopy. The average size of the NPs is in the range of 10–20 nm and lattice spacing is 0.36 nm corresponding (101) plane. The absorption and photoluminescence (PL)-excitation spectra of metal-doped TiO2 NPs are shifted to the longer wavelength region, which indicates reduced bandgap than the bare TiO2 NPs. The absorption and PL spectra of methylene blue (MB) in the presence of undoped and metal ions doped TiO2 NPs show dramatic changes upon UV-irradiation. The absolute absorption intensity reduced entirely and the solution of MB became colorless in the presence of UV irradiation. The PL of the degraded dye exhibits a new band in the shorter wavelength region, which has a multi-exponential decay function and an increased average PL lifetime. Among all the samples, Cu2+ ions-doped TiO2 NPs shows the superior photocatalytic activity for the degradation of dye and followed pseudo-first-order kinetics.

Rapid sensing of lead metal ions in an aqueous medium by MoS2 quantum dots fluorescence turn-off

The traditional methods used for the detection of heavy metal ions in an aqueous medium have been considered as complicated and time-consuming; therefore, it is highly recommended to find a rapid and sensitive probe. The functionalized molybdenum disulfide (MoS2) quantum dots (QDs) were developed and used as a sensitive fluorescent probe for monitoring the lead (Pb2+) ions in an aqueous medium. Photoluminescence (PL)/fluorescence intensity of the QDs strongly quenched in the presence of Pb2+ ions. The responsiveness of PL of QDs with Pb2+ in the range of 33 μM to 8.0 mM makes it a wide dynamic range sensing probe with a limit of detection (LOD) of 50 μM. Besides, the linear dependence of an absolute absorption intensity with the concentration of Pb2+ ions makes it a significant probe for monitoring the lead metal ions in an aqueous environment.

基于TDLAS的气体检测技术算法

Tunable diode laser absorption spectroscopy(TDLAS) is a high sensitive and high resolution gas absorption spectrum detection technology, with fast response, high precision, excellent single mode characteristics and strong versatility. The temperature and concentration of the detected gas were calculated by measuring the absolute absorption intensity in the direct absorption method of TDLAS, but was easily affected by particle concentration and fluctuation of laser intensity. The laser was modulated through high frequency sinusoidal signal in the wavelength modulation method of TDLAS, making the laser output frequency and intensity modulated simultaneously, with the characteristics of high signal-to-noise ratio and sensitivity, but the gas parameters were determined by calibration experiments or complex algorithms. Therefore, the expression of harmonic terms containing molecular absorption information was deduced through the theory of absorption spectrum and wavelength modulation, and the relationship between harmonic signal and absolute absorption intensity of detected gas was analysed, establishing the measurement algorithm of absolute absorption intensity based on harmonic signal. The absorption spectral line of NH3 molecule near 1 531 nm was taken as an example for numerical analysis, and the relative errors between theoretical calculation (a=0) and simulation values were no more than 2% when the modulation amplitude reached up to a=0.032 cm-1(m=2), which further proved the reliability of on-line measurement algorithm.

Experimental and theoretical studies of excited states of H2 observed in the absorption spectrum: I. The 5pπD″ 1Πu state

The 5pπD″−X absorption lines of H2 have been reinvestigated using synchrotron radiation with a resolution of 0.001nm, in an experiment that also yields the absolute absorption intensity for each observed transition. New assignments have been made which extend the manifold of known levels up to the H(n=4)+H(1s) dissociation threshold. The observations are interpreted in the framework of Multichannel Quantum Defect Theory (MQDT), implemented here in a pure first principles approach based on the best available quantum chemical clamped-nuclei potential energy curves of Wolniewicz and collaborators [1,2]. The approach provides theoretical values for the transition energies, intensities, natural widths and quantum yields. Very good agreement is found in general between experiment and theory (to within ≈1–2cm−1 for the transition energies). An exception concerns the 5pπ, v=2, N=2 positive total parity state for which the ionization width is calculated by 40% too large.

On the accuracy of ab initio calculations of absolute band intensities in the IR spectra of molecules

Absolute intensities are calculated in the harmonic approximation for the IR spectrum of 18 hydrocarbons, oxygen- and nitrogen-containing organic compounds. The quantum chemical calculation is carried out in the 6-311G(3df,3pd) basis set. The calculated data are compared to the experimental values of absolute absorption intensities. It is found that calculations in the HF approximation substantially overestimate (on average by 87%) the integral absolute intensity of fundamental vibrations in the 575–4000 cm−1 range. Most part of this overestimation falls on the stretching vibrations with large amplitudes (C-H and C=O bonds). When the MP2 method is used without electron correlation treatment, this overestimation decreases to 22% and becomes more uniform in the whole spectral region.

Ab initio calculation of band absolute intensities in IR spectra

Ab initio calculations in a harmonic approximation of absorption band absolute intensities in infrared spectra were carried out for 3 hydrocarbons and 14 halogenated hydrocarbons. The calculated data were compared with experimental values of the absolute absorption intensities. It is shown that a Hartree–Fock calculation method overestimates significantly (by an average of 66%) the integrated absolute intensities of the fundamental bands in the region 575–4000 cm–1. The deviation is reduced to 32% in the case of the MP2 method of accounting for electron correlations. Most of the overestimation occurs for bands corresponding to vibrations involving halogen atoms.

The infrared spectrum of cyclic-N3: Theoretical prediction

We have carried out the first calculations of the infrared absorption spectrum of cyclic-N(3). Accurate vibrational energies and wave functions computed with incorporation of the geometric phase effect (via gauge theory) and using an ab initio potential energy surface were employed in this work. A sophisticated fully dimensional dipole moment function was constructed using accurate ab initio calculations and a three-dimensional-spline interpolation. Transformation of the dipole moment vector function from the reference frame associated with instantaneous principal axes of inertia to the laboratory-fixed reference frame was carried out using hyperspherical coordinates. We found that the permanent dipole moment of cyclic-N(3) in the ground vibrational state is relatively small (170 mD). The excited vibrational states show permanent dipole moments in the 10-25 mD range. The most intense part of the infrared absorption spectrum is observed in the deep infrared part of spectrum, 75-275 cm(-1), where five lines exhibit absolute absorption intensities in the range between 0.5 and 1.2 km/mol. These transitions correspond to excitation of the pseudorotational progression of states. Several unique spectroscopic features discussed in the paper should help to identify cyclic-N(3) in the laboratory.

Intensity of d−d Symmetry-Forbidden Electronic Transition in Cr(CO)6

Absolute absorption intensities (oscillator strengths) are calculated for the d-d symmetry-forbidden transition in hexacarbonyl chromium. The vibronic coupling mechanism is taken into account in a way that represents an alternative to the traditional perturbative approach of Herzberg and Teller. In the so-called direct method, the electronic transition moment is directly expanded in a power series of the vibrational normal coordinates of suitable symmetry. In the present case, i.e., d-d ligand field transitions, or more specifically (1)A(1g) --> (1)T(1g) and (1)A(1g) --> (1)T(2g) transitions, the dipole selection rule is broken by vibronic interaction induced by normal modes that transform like T(1u) and T(2u) representations of the O(h) group. An analysis of the relative importance of normal modes in promoting electronic transitions is carried out.

Ab initio prediction of the infrared-absorption spectrum of the C2Cl radical

The three lowest (1(2)A', 2(2)A', and 1(2)A") potential-energy surfaces of the C2Cl radical, correlating at linear geometries with 2Sigma+ and 2Pi states, have been studied ab initio using a large basis set and multireference configuration-interaction techniques. The electronic ground state is confirmed to be bent with a very low barrier to linearity, due to the strong nonadiabatic electronic interactions taking place in this system. The rovibronic energy levels of the 12C12C35Cl isotopomer and the absolute absorption intensities at a temperature of 5 K have been calculated, to an upper limit of 2000 cm(-1), using diabatic potential-energy and dipole moment surfaces and a recently developed variational method. The resulting vibronic states arise from a strong mixture of all the three electronic components and their assignments are intrinsically ambiguous.

Overtone-Induced Chemistry of Trifluoroacetic Acid: An Experimental and Theoretical Study

The effect of overtone-induced chemistry on the atmospheric fate of trifluoroacetic acid has been investigated. We report the absolute absorption intensities for the vOH = 3, 4, and 5 overtone transitions as well as an ab initio calculation of the energetics of the dissociation pathways. Calculations at the MP2 level give the lowest dissociation barrier as 50.3 kcal mol-1 for the elimination of HF. Integrated cross sections for vOH = 3, 4, and 5 are 2.70 × 10-20, 1.68 × 10-21, and 1.5 × 10-22 cm2 molecule-1 cm-1, respectively. Dissociation may proceed after absorption into v = 5 or 6, giving an upper limit to the photodissociation rate constants of 3.7 × 10-9 s-1 or 2.5 × 10-10 s-1, respectively. These correspond to a tropospheric lifetime of between 8 and 127 years. The overtone-driven photodissociation is more important than the ultraviolet photodissociation in the troposphere but is insignificant in comparison to wet deposition and the reaction with OH radicals.

High-Resolution Spectroscopic Study of Matrix-Isolated Reactive Intermediates: Vibrational Assignments for 3-Fluoro-o-Benzyne and Perfluoro-o-Benzyne∇

A novel “site decompression technique” that takes advantage of specific pressure relaxation effects in cryogenic noble gas matrices was applied in a spectroscopic investigation of the two title compounds, resulting in virtually background-free, complete, high-resolution IR spectra with line widths of ca. 0.1 cm-1. The compounds were prepared photochemically in Ar and Ne matrices and, together with the related intermediates, fluorinated benzocyclopropenone and cyclopentadienylideneketene, characterized by IR and UV−visible absorption spectroscopy. Weak IR absorption bands observed at 1878 cm-1 for perfluoro-o-benzyne and at 1866 cm-1 for 3-fluoro-o-benzyne were assigned to CC triple bond stretching vibrations, corresponding to the transition at 1846 cm-1 in the parent o-benzyne. The application of polarization spectroscopy on photooriented samples led to the determination of transition moment directions for most of the observed vibrational transitions. Absolute IR absorption intensities were also obtained. The assignments of the observed transitions were supported by the results of B3LYP/cc-pVDZ quantum chemical calculations.

Computer programs for the determination of optical constants from transmission spectra and the study of absolute absorption intensities

FORTRAN computer programs used in the determination of optical constants and other physical properties from transmission measurements have been written by the Jones and Bertie research groups. Over the last several years, C++ has emerged as the standard programming language and it has become desirable to convert these programs. In this paper, C++ versions are presented and their accuracy is confirmed. In addition, some new features have been added to some of the programs.

Quantum chemical B3LYP/cc-pvqz computation of ground-state structures and properties of small molecules with atoms of Z ≤ 18 (hydrogen to argon)(IUPAC Technical Report)

Abstract Since density functional theory (DFT) achieved a remarkable break-through in computational chemistry, the important general question "How reliable are quantum chemical calculations for spectroscopic properties?" should be answered anew. In this project, the most successful density functionals, namely the Becke B3LYP functionals, and the correlation-consistent polarized valence quadruple zeta basis sets (cc-pvqz) are applied to small molecules. In particular, the complete set of experimentally known diatomic molecules formed by the atoms H to Ar (these are 214 species) is uniformly calculated, and calculated spectroscopic properties are compared with experimental ones. Computationally demanding molecules, such as open-shell systems, anions, or noble gas compounds, are included in this study. Investigated spectroscopic properties are spectroscopic ground state, equilibrium internuclear distance, harmonic vibrational wavenumber, anharmonicity, vibrational absolute absorption intensity, electric dipole moment, ionization potential, and dissociation energy. The same computational method has also been applied to the ground-state geometries of 56 polyatomic molecules up to the size of benzene. Special sections are dedicated to nuclear magnetic resonance (NMR) chemical shifts and isotropic hyperfine coupling constants. Each set of systems for a chosen property is statistically analyzed, and the above important question "How reliable...?" is mathematically answered by the mean absolute deviation between calculated and experimental data, as well as by the worst agreement. In addition to presentation of numerous quantum chemically calculated spectroscopic properties, a corresponding updated list of references for experimentally determined properties is presented.

The vibrational spectrum of pyrrole (C 4H 5N) and furan (C 4H 4O) in the gas phase

We have recorded the absorption spectrum of pyrrole (C 5H 5N) and furan (C 4H 4O) on a broad spectral range in the infrared region and under various experimental conditions, using a Fourier transform interferometer. The resolution was good enough to reliably identify band shapes. We have performed the vibrational assignment of the vibration–rotation bands observed between 500 and 12,000 cm −1 for pyrrole, and 500 and 9000 cm −1 for furan. The assignment of the fundamental bands is supported by ab initio calculations at the MP2 level of approximation, considering both band positions and absolute absorption intensities. These calculations also allowed the normal mode coordinates to be drawn for the two species and their geometrical structure to be calculated. Vibrational mode numbering and symmetries are updated to latest conventions in the literature. In the combination and overtone spectral ranges, the band shape information guided the assignment, which could be achieved for most of the numerous observed bands. An extensive set of vibration constants was obtained for each species. The results from the literature available on each species are considered at each step of the investigation.

Intensity of the [formula omitted] symmetry-forbidden electronic transition in acetone by direct vibronic coupling mechanism

Absolute absorption intensities were calculated for the symmetry dipole forbidden n→ π ∗ transition in acetone. An analysis of the distribution per normal modes is performed and the results are compared with a recent calculation. Vibronic coupling mechanism is taken into account in a way that is different from the traditional Herzberg–Teller perturbation approach. In the present method the electronic transition moment is directly expanded in power series of the vibration normal coordinates. This approach was recently used for the equivalent n→ π ∗ transition in formaldehyde presenting an excellent agreement with the experimental results.

FT‐IR measurements of petroleum fluid inclusions: methane, n‐alkanes and carbon dioxide quantitative analysis

AbstractA recent advancement in petroleum geochemistry is to model fossil oil composition using microthermometric and volumetric data acquired from individual fluid inclusion analysis. Fourier transform infrared (FT‐IR) microspectroscopy can record compositional information related to gas (CH4 and CO2) and alkane contents of petroleum inclusions. In this study, a quantitative procedure for FT‐IR microspectrometry has been developed to obtain, from individual fluid inclusions, mol percentage concentrations of methane, alkanes and carbon dioxide as constraints to thermodynamic modelling. A petroleum inclusion in a sample from the Québec City Promontory nappe area was used as standard to record a reference spectrum of methane. The analytical procedure is based on the measurement of CH4/alkane and CH4/CO2 band area ratios. CH4/alkane infrared band area ratio is obtained after spectral subtraction of the reference methane spectrum. This area ratio, affected by absolute absorption intensities of methane, methyl and methylene, provides a molar CH4/alkane ratio. Methyl/methylene ratio (CH2/CH3) ratio is obtained following procedures established in previous work. CO2/CH4 concentration ratio is estimated from relative absolute absorption intensities. Application to natural inclusions from different environments shows good correlation between FT‐IR quantification and PIT (petroleum inclusion thermodynamic) modelling.

Resonance Raman intensity analysis investigation of metal-metal bonded transitions: an examination of the1A2u ←1A1g (5dσ* → 6pσ) transition of Pt2(P2O5H2)44−

A preliminary resonance Raman intensity analysis study of the 1A2u← 1A1g (5dσ*→ 6pσ) transition of (n-Bu4N)4[Pt2(P2O5H2)4] in acetonitrile solution at room temperature is reported. The absolute resonance Raman and absorption intensities were simultaneously simulated using wavepacket calculations and a simple model. The best fit parameters indicate that the Pt— Pt bond length changes by about 0.225 Å in the initially excited 1A2u state relative to the ground state. This is in good agreement with previous studies on the vibronically structured absorption and emission spectra of low-temperature crystalline (n-Bu4N)4[Pt2(P2O5H2)4] which suggested that the Pt— Pt bond length changes by about 0.21 Å in the 1,3A2u states. The resonance Raman intensity analysis demonstrated here can be generally applied to metal– metal bonded electronic transitions for compounds and sample conditions (such as room temperature liquids for many samples) which do not exhibit any vibronic structure. Copyright © 1999 John Wiley & Sons, Ltd.