Absorption Band Profile Research Articles

The Fabry-Perot effect suppression in gas cells used in THz absorption spectrometers

Gas cells are widely used in THz and IR absorption spectroscopy. However, reflections of an optical wave on cell input and output windows cause a gas sample measured spectrum distortion due to the Fabry-Perot effect. The hardware approach to decrease the Fabry-Perot effect in the THz spectral range is suggested. The approach is based on using a standard gas cell and the additional movable optically transparent window. To illustrate usefulness of the suggested approach, a simulation of registration of the sulfur dioxide absorption band near 660 GHz in the gas mixture consisted of 0.1 % SO2 and 99.9 % N2 was conducted. The absorption band profile fluctuations due to the Fabry-Perot effect were shown to be reduced by almost 4 times with the suggested approach implementation in relation to the default gas cell. This approach can be combined with other hardware and software variants of the Fabry-Perot effect suppression.

Ultraviolet electronic spectroscopy of heavily substituted naphthalene derivatives

Context. The so-called bump spectral signature observable on interstellar extinction curves, peaking at 217.5 nm, is commonly assigned to π* ← π transitions from carbonaceous carriers, but the exact nature of the carbonaceous carriers remains debated. Aims. To constrain the chemical structures associated with the bump carriers, we record and compare the UV spectra of a large variety of carbonaceous molecules to this interstellar feature. Methods. Large carbonaceous molecules, such as polycyclic aromatic hydrocarbons (PAHs), were produced by a combustion process stabilized at low pressure under rich flame conditions. Species were extracted and probed through resonance enhanced multiphoton ionization spectroscopy coupled to a time-of-flight mass spectrometer. Masses and absorption profiles of the carbonaceous molecules were measured, and their spectra were compared to the bump feature. Results. Species showing a specific mass progression starting at mass 128 u visible up to mass 394 u with a characteristic progression of +14 u present a common electronic absorption band profile peaking asymptotically around 220 nm. The first masses were assigned to a naphthalene C10H8 molecule and two of its derivatives: C10H7CH3 and C10H7C2H5. The mass progression of +14 u is explained by successive H atom substitutions by CH3 functional groups. This mass distribution was thus assigned to naphthalene derivatives with large aliphatic carbon substitution. This derivative family shows an electronic band assigned to S3 ← S0 transitions involving electron promotion within the π aromatic orbitals of the naphathlene chromophore. More importantly, after a few substitutions, the position of the band converges asymptotically to a value close to the interstellar bump signature, independent of the molecule size. Conclusions. Based on the asymptotic behavior of the larger members in the species distribution, a similar band position is expected from double aromatic ring substructures within hydrogenated amorphous carbons (HACs). Similar to the conclusions of previous works, we find substituted naphthalene units as substructures of interstellar HACs to be good candidates as carriers of the bump feature.

Revision of the 60-GHz atmospheric oxygen absorption band models for practical use

Two models for millimeter-wave absorption by molecular oxygen in the air are updated. To derive the updated parameter set, earlier resonator spectrometer data are refined and recent data on the collisional parameters’ temperature behavior are taken into account. The updated models provide significantly better agreement between laboratory measurements and calculated absorption band profiles than their earlier versions. The predictive ability of the models is confirmed by new experimental data. The covariance matrix of empirical parameter uncertainties, together with absorption-calculation uncertainty, are evaluated for both updated models. Contributions of the various sources to the total calculation uncertainty are discussed.

Dome C ultracarbonaceous Antarctic micrometeorites

Context.UltraCarbonaceous Antarctic MicroMeteorites (UCAMMs) represent a small fraction of interplanetary dust particles reaching the Earth’s surface and contain large amounts of an organic component not found elsewhere. They are most probably sampling a contribution from the outer regions of the solar system to the local interplanetary dust particle (IDP) flux.Aims.We characterize UCAMMs composition focusing on the organic matter, and compare the results to the insoluble organic matter (IOM) from primitive meteorites, IDPs, and the Earth.Methods.We acquired synchrotron infrared microspectroscopy (μFTIR) andμRaman spectra of eight UCAMMs from the Concordia/CSNSM collection, as well as N/C atomic ratios determined with an electron microprobe.Results.The spectra are dominated by an organic component with a low aliphatic CH versus aromatic C=C ratio, and a higher nitrogen fraction and lower oxygen fraction compared to carbonaceous chondrites and IDPs. The UCAMMs carbonyl absorption band is in agreement with a ketone or aldehyde functional group. Some of the IR and Raman spectra show a C≡N band corresponding to a nitrile. The absorption band profile from 1400 to 1100 cm-1is compatible with the presence of C-N bondings in the carbonaceous network, and is spectrally different from that reported in meteorite IOM. We confirm that the silicate-to-carbon content in UCAMMs is well below that reported in IDPs and meteorites. Together with the high nitrogen abundance relative to carbon building the organic matter matrix, the most likely scenario for the formation of UCAMMs occurs via physicochemical mechanisms taking place in a cold nitrogen rich environment, like the surface of icy parent bodies in the outer solar system. The composition of UCAMMs provides an additional hint of the presence of a heliocentric positive gradient in the C/Si and N/C abundance ratios in the solar system protoplanetary disc evolution.

The 9577 and 9632 Å Diffuse Interstellar Bands: as Carrier

Abstract Galazutdinov et al. (2017) recently claimed that the relative strengths of the 9577 and 9632 Å diffuse interstellar bands (DIBs) are too poorly correlated to be caused by a single source, the ion. Their conclusion is based on theoretical modeling of contaminating stellar Mg ii lines at 9631.9 and 9632.4 Å and UVES spectra. This contradicts their earlier result and those of several others that the two DIBs are closely correlated and, within the errors and effects of stellar blends, exhibit an intensity ratio consistent with that found in the 6 K laboratory spectrum of . We consider the use of close spectral standards to be superior to model atmosphere calculations in correcting for contamination by the Mg ii lines. We have examined some of the same UVES spectra and demonstrate that a lack of suitably observed telluric standards makes it impossible to adequately correct for telluric water vapor contamination, leading to unreliable continuum levels. The possible effects of higher temperatures, in the 30–100 K range, on the electronic absorption band profiles, and their relative intensities, are also considered.

Optical and dielectric properties of transparent ZrO2–TiO2–Li2B4O7 glass system

Abstract A new series of transparent zirconium titanium lithium diborate glasses of the nominal composition 85 Li 2 B 4 O 7 –(15–x) TiO 2 – x ZrO 2 (x = 0, 5, 10 and 15 mol %) was prepared using melt quenching method. The investigated glasses are characterized in an attempt to determine the effect of different zirconium ion concentrations on their structural, optical and dielectric properties. X-ray diffraction (XRD) patterns confirmed the amorphous nature of the present glass system. The main features concerning the local structure of the present glass system were determined by Fourier transform infrared (FTIR) spectroscopy. The addition of Zr ions to borate glass changed the coordination of borate matrix and consequently converted BO 4 to BO 3 (BO 4 →BO 3 back conversion effect). Optical transmission and reflection measurements were performed as a function of wavelength, showing highly transparent glasses. The optical constants such as refractive index, extinction coefficient, absorption coefficient and optical band gap were calculated. The actual value of the optical band gap energy for these glasses was established by studying the absorption band profile. The frequency and temperature dependent dielectric constant, dielectric loss and AC electrical conductivity measurements were carried out. Excellent structural and physical, optical and dielectric properties of the present glass system indicate prospects for various photonic devices.

Molecular excitons in a copper azadipyrrin complex.

Exciton coupling is investigated in a copper azadipyrrin complex, Cu(L-aza)2. Exciton coupling in Cu(L-aza)2 assuming a single π-π* state on the L-aza ligand fails to account for the electronic structure of Cu(L-aza)2, which displays two almost equal intensity transitions at 15 600 cm(-1) and 17 690 cm(-1). TD-UB3LYP/6-31G(d) calculations suggest multiple π-π* transitions for the L-aza ligands and simple vector addition of the transition dipoles predicts two nearly orthogonal co-planar excitonic transitions that correctly reproduce the absorption band profile. Empirical modelling of absolute resonance Raman intensities using wavepacket dynamics confirms Cu(L-aza)2 has two equal intensity orthogonal exciton transitions. The phenyl substituents at the α- and γ-positions of the pyrrole rings play a central role in determining the orientation of the transition dipoles. Consequently the π-π* transitions for the L-aza ligands are oriented towards the substituent groups and are not in the plane of the pyrrole rings. Mode displacements in the Franck-Condon (FC) region obtained from the wavepacket model suggest that pyrrole ring and phenyl modes control the exciton FC dynamics. Our results suggest that Cu(L-aza)2 is an ideal model for theoretical, computational and experimental investigations of molecular excitons in molecular systems.

Laboratory spectra of CO2 vibrational modes in planetary ice analogs

Laboratory spectra have shown that CO2 is a powerful diagnostic tool for analyzing infrared data from remote observations, as it has been detected on icy moons in the outer Solar System as well as dust grain surfaces in the interstellar medium (ISM). IR absorption band profiles of CO2 within ice mixtures containing H2O and CH3OH change with respect to temperature and mixture ratios. In this particular study, the ν3 CO2 asymmetric stretch mode near 4.3μm (2350cm−1), overtone mode near 1.97μm (5080cm−1), and the combination bands near 2.7μm (3700cm−1), 2.8μm (3600cm−1), and 2.02μm (4960cm−1), are systematically observed in different mixtures with H2O and CH3OH in temperature ranges from 15K to 150K. Additionally, some high-temperature deposits (T>50K) of H2O, CH3OH, and CO2 ice mixtures were performed and it was discovered that CO2 may deposit out at higher temperatures than previously recorded. These data may then be used to interpret infrared observational data obtained from icy surfaces in the outer Solar System and beyond.

Surprising stability of the trion against the free carrier screening

AbstractThe effects of charge‐density fluctuations on trion states and spin‐density fluctuation on the exciton states in quantum well are considered in the limit of low doping by electrons. In both cases the quasi‐two dimensionality of the systems is taken into account. The trion‐chargedensity interaction is considered in the random phase approximation.The influence of the exchange electron‐electron interaction on the excitons is considered using a simplified approach. It is shown that the broadening of the trion absorption band profile with free carrier concentration increase is essentially weaker than the broadening of the exciton absorption band. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

C2in Peculiar DQ White Dwarfs

White dwarfs (WDs) with carbon absorption features in their optical spectra are known as DQ WDs. The subclass of peculiar DQ WDs are cool objects ( -->Teff 6000 K) that show molecular absorption bands that have centroid wavelengths ~100-300 A shortward of the bandheads of the C -->2 Swan bands. These peculiar DQ bands have been attributed to a hydrocarbon such as C -->2H. We point out that C -->2H does not show strong absorption bands with wavelengths matching those of the peculiar DQ bands, and neither does any other simple molecule or ion likely to be present in a cool WD atmosphere. C -->2 seems to be the only reasonable candidate for producing the peculiar DQ bands. Many characteristics of those bands can be understood if they are pressure-shifted Swan bands. While current models of WD atmospheres suggest that, in general, peculiar DQ WDs do not have higher photospheric pressures than normal DQ WDs do, that finding requires confirmation by improved models of WD atmospheres and of the behavior of C -->2 at high pressures and temperatures. If it is eventually shown that the peculiar DQ bands cannot be explained as pressure-shifted Swan bands, the only explanation remaining would seem to be that they arise from highly rotationally excited C -->2 ( -->Jpeak 45). In either case, the absorption band profiles can in principle be used to constrain the pressure and the rotational temperature of C -->2 in the line-forming regions of normal and peculiar DQ WD atmospheres, which will be useful for comparison with models. Finally, we note that progress in understanding magnetic DQ WDs may require models that simultaneously consider magnetic fields, high pressures, and rotational excitation of C -->2.

On the water dimer contribution to the OH stretching absorption band profile in pressurized water vapour

The present paper considers the density effect on the water vapour absorption profile in the OH stretch range. The density evolution of the water vapour OH fundamental band shape is interpreted in terms of the monomer–dimer equilibrium. In contrast to previous works we adopt experimental values for the frequencies and IR intensities of the dimer vibrations in the vicinity of 3µm. This made it possible to reduce the number of unknown parameters required in the course of our spectral fit.

Aspects of hole burning and spectro-temporal holography in molecular doped solids (Review)

The persistent spectral hole-burning (PSHB) phenomenon has been known since 1974. It is still an important research area for the study of the intimacy of complex molecular systems in the solid state, revealing high-resolution spectra, photophysics, photochemistry, and dynamics of molecular doped amorphous media, organic as well as inorganic. From another point of view, PSHB allows the engraving of any spectral structures in the inhomogeneous absorption band profile of molecular doped amorphous hosts or ion doped crystals cooled down to liquid helium temperatures. Therefore, a PSHB material is programmable in the spectral domain and consequently it can be transformed in an optical processor capable of achieving user-defined optical functions. Some aspects of both fields are illustrated in the present paper. Concerning the search for efficient PSHB materials, the hole-burning performances and the photophysics of polymer and xerogel based systems are compared. The problem of high-temperature persistent spectral hole-burning materials and the search for new frequency selective photosensitive systems for fast optical pulse processing at 800nm are considered. Regarding the points treated, inorganic hosts based on silicate xerogels or porous glasses have shown the best results. Moreover, by combining inorganic and organic capabilities or by grafting organic species to the host, hybrid xerogels have not yet revealed all possibilities. Also, the interest of two-photon materials for engraving spectral features with near-infrared or infrared light is developed. As an introduction to possible applications of PSHB material, the basics of spectro-temporal holography are remembered and a demonstrative experiment using a naphthalocyanine-doped polymer film is described, proving that the temporal aberration free recompression of ultrashort light pulses is feasible, therefore opening a way for applications in ultrashort light pulse shaping. Aspects for a comparison between cw hole-burning and femtosecond spectro-temporal experiments are considered, and prospects for coherent control of light fields or photochemical processes are also evoked.

Photophysical and electrochemical studies of heteroleptic cyclometallated complexes of rhodium(III) containing 2-benzoylpyridine

Two heteroleptic cyclometallated complexes, cis-[Rh(bzpy)(bipy)Cl 2] ( 1) and cis-[Rh(bzpy)(phen)Cl 2] ( 2) (where bzpy = 2-(2-pyridylcarbonyl)phenyl, bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline) have been synthesized and characterized. Based on IR and NMR data, it is evident that the coordinated bzpy ligand is N, C coordinated with Rh(III). Each complex shows high intensity bands in the UV region, assigned as spin-allowed π–π ∗ transitions. The medium-intensity absorption band profile in the lower energy region can be explained by convolution of carbonyl n–π ∗ and d–d ∗ transitions. At low temperature (77 K), each complex shows a broad, symmetric and structureless red emission with a microsecond lifetime and, hence, is assigned as dd ∗ phosphorescence. Voltammetric data have also been obtained for both complexes. There were two reduction peaks observed for each complex. The first reduction peak involves the transfer of two electrons and the elimination of two chlorides. The redox orbital involved in the second reduction is assigned to be the π ∗ orbital localized on the carbonyl fragment of bzpy by examination of the influence on the reduction potentials in the presence of phenol.

Infrared extinction by homogeneous particle aggregates of SiC, FeO and [formula omitted]: Comparison of different theoretical approaches

Particle shape and aggregation have a strong influence on the spectral profiles of infrared phonon bands of solid dust grains. Calculating these effects is difficult due to the often extreme refractive index values in these bands. In this paper, we use the discrete dipole approximation (DDA) and the T-matrix method to compute the absorption band profiles for simple clusters of touching spherical grains. We invest reasonable amounts of computation time in order to reach high dipole grid resolutions and take high multipolar orders into account, respectively. The infrared phonon bands of three different refractory materials of astrophysical relevance are considered—silicon carbide, wustite and silicon dioxide. We demonstrate that even though these materials display a range of material properties and therefore different strengths of the surface resonances, a complete convergence is obtained with none of the approaches. For the DDA, we find a strong dependence of the calculated band profiles on the exact dipole distribution within the aggregates, especially in the vicinity of the contact points between their spherical constituents. By applying a recently developed method to separate the material optical constants from the geometrical parameters in the DDA approach, we are able to demonstrate that the most critical material properties are those where the real part of the refractive index is much smaller than unity.

Photochemistry of formaldehyde under tropospheric conditions

We report new results on the absorption cross sections and photochemical quantum yields for radical (H + HCO) production from formaldehyde in the wavelength interval from 308-320 nm, obtained at resolutions of better than 0.1 nm. The absorption cross sections, measured at resolutions close to the limit for Doppler broadening of HCHO, show rotationally resolved fine structure, with maximum values higher than those obtained in previous, lower resolution, studies. In this wavelength region, absorption cross sections peak at 2.3 x 10(-19) cm2 molecule(-1), but band-integrated values are in excellent accord with previous measurements. HCO absorption coefficients, measured by cavity ring-down spectroscopy following UV photolysis of HCHO at wavelengths across the 2(0)(1)5(0)(1), 2(0)(2)4(0)(3) and 2(0)(3)4(0)(1) bands of the A1A2-X1A1 transition, generally mimic the parent absorption band profiles. Division of these absorption coefficients by the high resolution parent absorption cross sections gives relative quantum yields for the H + HCO radical product channel that can be put on an absolute scale using single-wavelength literature values. These quantum yields are observed to show some variation with parent excitation wavelength (and thus with excited vibronic level). Addition of 200 Torr of N2 increases the HCO quantum yields.

Synthesis and spectral properties of 2-pyridyl N-methyl-2-imidazolyl ketone complexes of iridium(III)

Complexes of iridium(III) with 2-pyridyl N-methyl-2-imidazolyl ketone (pik), K[Ir(pik)Cl 4] ( 1) and [Ir(pik)(phen)Cl 2] + ( 2), have been successfully prepared and characterized. Both complexes show high intensity bands in the UV region, and these are assigned to spin-allowed π–π* transitions. The medium-intensity absorption band profile in the lower energy region can be explained by spin-allowed CT and, perhaps, convoluted with the weaker n–π* transitions. At low temperature (77 K), complex 2 in EtOH/MeOH (4:1, v/v) shows a structural emission with a single vibrational progression of 1090 cm −1. The luminescence lifetime measured at 474 nm ( ν max, 0–0′ band) emission is 9.7 μs and the emission energy becomes smaller while the polarity of solvent increases. Electrochemical data have also been obtained for complex 2 in MeCN. There were two reduction peaks observed for the complex and both are one-electron charge transfer process. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in each of the reduction processes is assigned to be the π* orbital localized at the carbonyl fragment of pik. On the basis of analysis of the luminescence and electrochemical data, the emission of complex 2 is assigned as 3MLCT, with a charge transfer to the accepting pik π* orbital.

Synthesis and Photophysical Properties of Hetero‐Bischelated Complexes of Rhodium(III) Containing Phenyl‐Pyridin‐2‐Ylmethylene‐Amine

AbstractThree new hetero‐bischelated rhodium (III) complexes of cis‐[Rh(PA)(L)Cl2]Cl (where PA = phenylpyridin‐2‐ylmethylene‐amine; L = 2,2′‐bipyridine, 2,2′‐dipyridylamine and 1,10‐phenanthroline) have been successfully prepared and characterized. Each complex shows high intensity bands in the UV region, and these are assigned to spin‐allowed π‐π* transitions. The medium‐intensity absorption band profile in the lower energy region can be explained by convolution of spin‐allowed CT and d‐d* transitions. The emission spectra at low temperature (77 K) of these complexes in EtOH/MeOH (4:1 v/v) are virtually identical. They all exhibit a broad, symmetric, and structureless red emission with a microsecond lifetime and hence are assigned as the d‐d* phosphorescence.

Spectral and electrochemical properties of 2-pyridyl N-methyl-2-imidazolyl ketone complex of rhodium(III)

A new complex of [Rh(pik) 2Cl 2]Cl (where pik is 2-pyridyl N-methyl-2-imidazolyl ketone) has been synthesized and characterized. Both the free pik and the complex show high intensity bands in the UV region, and are assigned to spin-allowed π–π* transitions. Only the complex, however, exhibits medium-intensity absorption band profile in the lower energy region. This low-energy absorption might be explained by spin-allowed CT and, perhaps, convoluted with the weak d–d* transitions. Emission spectra at low temperature (77 K) of both the free pik and the complex in EtOH/MeOH (4:1 v/v) have also been investigated. The less structure spectrum observed for free pik is confirmed as n–π* transition. On the other hand, the complex shows a broad, symmetric, and structureless red emission with microsecond lifetime and hence is assigned as d–d* phosphorescence. Voltammetric data have also been obtained for free pik and the complex. The one-electron transfer occurred at the pi-system of the CO fragment of the free pik. There were three reduction peaks observed for the complex. The first peak, including two reduction steps with elimination of two chlorides, is consistent with ECEC reaction. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in the last reduction is assigned to be the π* orbital localized at the carbonyl fragment of pik.

Characterisation of LPCVD silicon oxynitride films by optical spectroscopy

The Si-H and Si-N vibration modes contributions to IR absorption bands in the wave number range of 600-960 cm -1 has been investigated for the as-deposited LPCVD SiON layers prepared at different N 2 O/ NH 3 ratios. The increasing of N/O atomic ratio was related to the specific changes of the wide IR absorption band profile. The variation of the Si-O bonds population in the oxynitride films deposited on c-Si has been found by IR spectroscopy after post thermal annealing at 1050°C in wet O 2 . The Si-O bonding in SiON film has been related to a sequence of two steps, indicated by the time dependency of the integral absorption band of the asymmetric stretching vibration mode at 1075 cm -1 . We have found a fast increase of Si-O population after about 40 min of heating. The time dependency shows an almost a linear dependence versus t 1/2 . The break of the slope is produced only after a preliminary low rate increase process in Si-O bonding, roughly speaking being 20 times smaller than in the second process. The high rate of Si-O bond formation at long annealing times has been found to be related to the removal of the low frequency wing of the Si-H stretching absorption band at about 2100 cm -1 . This feature is also connected to the already reported Si-H frequency shift in local tetraedra as a result to Si-O bonding. The annealing behaviour of both, the real and the imaginary part of the refractive index n * (λ)=n(λ)+ik(λ) has been extracted using UV-VIS spectra simulation. The result indicates a systematic decrease of n and k with the heating time at 1050°C in wet O 2 , suggesting the increasing of oxygen content in SiON film. We have proposed a preliminary physical model for the Si-O bond formation in SiON at 1050°C in wet O 2 , based on two-step process. The first step assumes that at an early stage a local oxygen re-bonding to the tetraedra (like: Si[Si 2, A,H], where A can be N, OH, (NH) 2 , or H) changes the local chemical structure by breaking Si-Si bonds, especially close to the gas/solid interface. The partial reconstruction of SiON layer in a hot and wet O 2 atmosphere facilitates the incorporation of the oxidative species based on a diffusion limited process through a Si-O-Si network, embedded in the SiON film.

IR spectral density of weak H-bonded complexes involving damped Fermi resonances. II. Numerical experiments and physical discussion

The IR absorption band profile of the X–H stretching mode of weak H-bonded complexes involving Fermi resonances between the high frequency mode and some bending modes, all these modes being damped, have been computed within the linear response theory, by aid of the Fourier transform of the autocorrelation function of the dipole moment operator of the high frequency mode [O. Henri-Rousseau, D. Chamma, Chem. Phys. 229 (1998) 37]. As it appears the probability to observe realistic and noticeable modifications of the experimental lineshapes by Fermi resonances is strongly enhanced by the presence of an hydrogen bond, leading to the conclusion that Fermi resonances must play a very general role in the lineshapes of H-bonds.