Structure Of Absorption Spectra Research Articles

Dynamic Evolution from Chain Disorder to Order of PTB7 Condensed State Structures under External Fields.

In this research, the effect of external fields (solvent, temperature, solution concentration, and external force) on dynamic evolution from chain disorder to order of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2- b:4,5- b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4- b]thiophenediyl]] (PTB7) condensed state structures was explored by UV-vis absorption spectra, atomic force microscope, and transmission electron microscopy (TEM). It was found that PTB7 main chains presented amorphous conformations induced by the poor solvent 1,2-dichloroethane. However, the local ordered aggregation appeared in amorphous conformations when the solubility of the poor solvent was again lowered by reducing temperature. It is worth noting that the size of ordered aggregation was further increased with the decrease of solution concentration or increase of external force. It was found that there were two main PTB7 absorption peaks in the UV-vis absorption spectra; we denoted A0-0 for the intensity of the lower energy absorption peak and A0-1 for the intensity of the higher energy absorption peak. The ratio R = A0-0/ A0-1 was used to characterize the dynamic evolution from disorder to order of the PTB7 condensed state structures in absorption spectra. It increased from 0.94 for PTB7 amorphous state to 1.25 for PTB7 large-size ordered aggregation. The dynamic evolution from chain disorder to order could also be distinctly observed by TEM. It was inferred that PTB7 condensed state structures (amorphous state, local ordered aggregation, and large-scale ordered aggregation) might exist simultaneously because of the complexity of copolymer conformations. This research is meaningful to establish physical basis for the molecule design and the synthesis of materials to enhance photoelectronic device efficiency based on condensed matter physics of conjugated polymer.

Effects of fine structure of absorption spectrum and spin-singlet on zero-field-splitting parameters for BaCrSi4O10 and AgGaSe2:Cr2+

The compounds doped with or containing Cr2+ ions are extensively used as optoelectronic and nonlinear optical materials, because they have special optical, magnetic and electric properties. These properties are very closely related to the absorption spectra and zero-field-splitting. The studies of the absorption spectra and zero-field-splitting are very important for realizing the doped microscopic mechanism and understanding the interaction between impurity ions and host crystals, and they may be useful to material designers. The concept of the standard basis adapted to the double group chain is adopted in the strong-field scheme by the crystal field theory. This concept emphasizes the standardization of the basis of the whole 3d4 configuration space including all spin states. Thus, the basis functions can be constructed according to each irreducible representation of the double group and each basis function has a certain expression. Each standard basis adapted to the double group chain can be built from the former by a linear transformation, which forms a basis chain. Thus, the complete energy matrix including spin singlet is constructed for Cr2+ ion in tetragonal symmetry environment in the strong-field-representation by the crystal field theory. The fine structures of absorption spectra and the spin-singlet contributions to zero-field-splitting parameters for BaCrSi4O10 and AgGaSe2:Cr2+ are studied by diagonalizing the complete energy matrix. The fine structures for the two systems and the zero-field-splitting parameters for BaCrSi4O10 are given theoretically for the first time. The fine structures are assigned by the irreducible representation of the group. The results show that the spin-singlet contribution to D is negligible, but the contributions to a and F are important. The contributions arise from the interaction of the spin quintuplets with both spin triplets and spin singlets via spin-orbit coupling. However, the selection rule of spin-orbit coupling shows that the spin singlets do not affect the quintuplets directly but indirectly via the spin triplets. Thus, all spin states should be considered to obtain more accurate zero-field-splitting values.

First-Order Phase Transition in Liquid Water in Terms of the Mode Structure of Absorption Spectrum in the Near-IR Range

Absorption spectra of liquid water H2O are investigated in the region 4500–5600 cm–1 at temperatures from –53.0 to +20.3°C. The absorption band is decomposed into component modes at (I) 4700, (II) 4890, (III) 5080, and (IV) 5200 cm–1 whose centers are shifted slightly with temperature. Modes (II), (III), and (IV) are present in the spectrum of liquid water, whereas modes (I), (II), and (III) are registered in the spectrum of ice. The appearance of the ordered crystalline lattice is characterized by the occurrence of low-frequency mode (I) and by the disappearance of high-frequency component (IV) of the water absorption band in the region 4500–5600 cm–1. The spectral regions and temperature ranges in which the structure is changed during phase transition are determined.

Optical absorption, induced bleaching, and photoluminescence of CdSe nanoplatelets grown in cadmium octanoate matrix

CdSe nanoparticles (NPs) are chemically synthesized in thermotropic ionic liquid crystalline (LC) phase of cadmium octanoate that was used as a nanoreactor. The nanocomposite samples are obtained by the rapid cooling of the LC phase to room temperature. Observed doublet structure in absorption spectra of the nanocomposites is characteristic for the two-dimensional CdSe nanoplatelets (NPLs). The thicknesses of the CdSe NPLs are 1.6, 1.9 and 2.3 nm as determined from the absorption spectra, and correspond to 4, 5 and 6 CdSe monolayers, respectively. Induced simultaneous bleaching of the doublet components observed under femtosecond laser excitation, as well as photoluminescence spectra and their kinetics are found compatible with the model of excitons with heavy- and light-hole valence bands confined in nanoplatelets.

State-to-state photodissociation dynamics of triatomic molecules: H2O in the B band

State-to-state photodissociation dynamics of H(2)O in its B band has been investigated quantum mechanically on a new set of non-adiabatically coupled potential energy surfaces for the lowest two (1)A' states of H(2)O, which are developed at the internally contracted multi-reference configuration interaction level with the aug-cc-pVQZ basis set. Quantum dynamical calculations carried out using the Chebyshev propagator yield absorption spectra, product state distributions, branching ratios, and differential cross sections, which are in reasonably good agreement with the latest experimental results. Particular focus is placed here on the dependence of various dynamical observables on the photon energy. Detailed analyses of the dynamics have assigned the diffuse structure in absorption spectrum to short-time recurring dynamics near the HOH conical intersection. The non-adiabatic dissociation to the ground state OH product via the HOH conical intersection is facile, direct, fast, and produces rotationally hot OH(X̃) products. On the other hand, the adiabatic channel on the excited state leading to the OH(Ã) product is dominated by long-lived resonances, which depend sensitively on the potential energy surfaces.

Dynamics of femtosecond-laser-ablated liquid-aluminum nanoparticles probed by means of spatiotemporally resolved X-ray absorption spectroscopy

We investigated spatiotemporal evolution of expanding ablation plume of aluminum created by a 100-fs, 1014–1015-W/cm2 laser pulse. For diagnosing dynamic behavior of ablation plume, we employed the spatiotemporally resolved X-ray absorption spectroscopy (XAS) system that consists of a femtosecond-laser-plasma soft X-ray source and a Kirkpatrick–Baez (K–B) microscope. We successfully assigned the ejected particles by analyzing structure of absorption spectra near the LII,III absorption edge of Al, and we clarified the spatial distribution of Al+ ions, Al atoms, and liquid droplets of Al in the plume. We found that the ejected particles strongly depend the irradiated laser intensity. The spatial distribution of atomic density and the expansion velocity of each type of particle were estimated from the spatiotemporal evolution of ablation particles. We also investigated a temperature of the aluminum fine particles in liquid phase during the plume expansion by analyzing the slope of the LII,III absorption edge in case of 1014-W/cm2 laser irradiation where the nanoparticles are most efficiently produced. The result suggests that the ejected particles travel in a vacuum as a liquid phase with a temperature of about 2500 to 4200 K in the early stage of plume expansion.

Cyanine Dyes: Fine Structures in Their Absorption Spectra

Absorption spectra were studied for two series of 3 cyanine dyes with varying length of conjugated hydrocarbon chains. Fine structures in absorption spectra were analyzed to determine its concentration dependence as the concentration of dyes were changed from 10–8 M to 10–4 M. In all 6 dyes studied, ratios of minor peaks to the major peak remained constant within the experimental error. These results indicate that the origin of the absorption fine structure is due to the electronic coupling, an intramolecular process, rather than the aggregates formation, an intermolecular process.

Multichannel linear detector for x-ray spectroscopy

This paper considers a new linear multichannel x-ray detector designed on the basis of a BLPP-369M4 silicon photodiode array (2612 photodiodes, array pitch 12.5 µm, height 4 mm, and dynamic range 104). The structure and characteristics of the multichannel detector are given, along with the Kα1,2, Kβ1, and Kβ5 x-ray emission lines and a K-edge absorption spectrum of metallic copper recorded on a universal URS-2I spectrometer using this detector. The resolution and the signal/noise ratio of these spectra are superior to those of spectra recorded by an SRPP-21 gas ionization counter at the same recording time. The detector has a spatial resolution of 20 µm and an x-ray detection limit to equal 1 quantum at λ = 1.54 A. It is suitable for studying the fine structure of absorption spectra at 1–10 A.

Light absorption spectrum of two-dimensional Mott insulators

We theoretically investigate the light absorption spectrum of two-dimensional (2D) Mott insulators. We employ the numerical diagonalization method to calculate the light absorption spectrum with using the effective Hamiltonian for the extended Hubbard model, which is valid when the on-site Coulomb interaction energy $U$ is much larger than the nearest-neighbor transfer integral $t$ and the nearest-neighbor Coulomb interaction energy $V$. For $V=0$, the absorption spectrum consists of a broad band with a width of about $16t$ and a sharp central peak, and the energy eigenstates contributing to the absorption spectrum do not have the antiferromagnetic (AF) spin order, when $U$ is sufficiently larger than $t$. These features result from the spin-charge interplay inherent in the very strong correlation region where charge transfer term is dominant. With decreasing $U∕t$, the peak structure in absorption spectrum becomes unclear and some low energy eigenstates have the AF spin order, as a result of the spin-spin interaction term. For large $V∕t$, the dominant peak arises in the lower energy region of the spectrum. A large number of holon-doublon bound states, which have nearly the same charge but different spin structures, are responsible for this peak, in contrast to the conventional exciton state. This is also in contrast to the charge bound states in one-dimensional (1D) Mott insulators, where a single energy eigenstate dominates the optical transition moment as a result of the spin-charge separation. The essentially different absorption spectra between the 1D and 2D Mott insulators originate from the difference in the coupling between spin and charge degrees of freedom.

Light absorption by polaritons in an interface layer with strong excitonic response: effects of retardation and total reflection

Light absorption spectra by interface layer with strong excitonic response in asymmetric dielectric environment are calculated for various angles of incidence of the external light. Appreciable frequency shift of the absorption resonances in the total reflection regime is found. It is shown that higher polarition modes may reveal themselves in absorption spectra of high-ordered excitonic layers with strong exciton-photon interaction. In this case, doublet and triplet structures of absorption spectra emerge for s- and p-polarized light, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis of 8,16-Ethanoretinals and Their Interactions with Apoprotein of Phoborhodopsin from Natronobacterium pharaonis

Several 8,16-Ethanoretinals 3 were synthesized from cyclohexanones. From the binding experiments of these analogs with apoprotein of phoborhodopsin, it was found that retinal was incorporated as 6s-trans conformation in the protein and the fine structure in absorption spectra of pigments were dependent on the coplanarity of the conjugated polyene structure in the chromophore. Keywords: ethanoretinal, retinal analog, phoborhodopsin, chromophore, s-trans conformation

Dynamic quasi-energy-band modulation and exciton effects in biased superlattices driven by a two-color far-infrared field: Disappearance of dynamic localization

A theoretical study of the optical and electronic properties of semiconductor superlattices in ac-dc fields, termed the dynamic Wannier-Stark ladder (DWSL), is done. The biased superlattices are driven by two far-infrared fields with different frequencies and relative phase of $\ensuremath{\delta}.$ Here, the frequency of the first laser is equal to the Bloch frequency ${\ensuremath{\omega}}_{B}$ of the system under study, while that of the second laser is equal to $2{\ensuremath{\omega}}_{B}.$ Quasienergies of the DWSL are calculated based on the Floquet theorem, and the associated linear photoabsorption spectra are evaluated. For $\ensuremath{\delta}=0,$ a gourd-shaped quasi-energy structure characteristic of both dynamic localization (DL) and delocalization (DDL), similar to the usual DWSL driven by a single laser, appears. By changing the ratio of the two laser strengths, however, the width of the quasi-energy band and the locations of both DL and DDL vary noticeably. As for $\ensuremath{\delta}\ensuremath{\ne}0,$ on the other hand, band collapse and the associated DL do not necessarily follow. In fact, DL vanishes and the quasi-energy degeneracy is lifted in a certain range of $\ensuremath{\delta}.$ Just DDL remains over the entire range of the laser strength, eventually resulting in a plateaulike band structure in the linear absorption spectra. The basic physics underlying this phenomenon, which can be readily interpreted in terms of a closed analytical expression, is that all quasi-energies for given crystal momenta are out of phase with each other as a function of laser strength without converging to a single point of energy. This is a feature of this DWSL which sharply distinguishes it from a conventional DWSL generated using a single laser to drive it. Furthermore, an exciton effect is incorporated with the above noninteracting problem, so that exciton dressed states are formed. It is found that this effect gives rise to more involved quasi-energy structures and a more pronounced release of the energy degeneracy of DL, leading again to the formation of a band structure in the absorption spectra. These are exclusively due to unevenly spaced exciton energy levels.

Modeling vibronic spectra and excited states of polyenes with a parametric method

The structural-dynamic models of excited states and vibronic structure of absorption spectra of linear polyenes (R-(CH=CH)n-R, R=H, CH3, n=4, 5, 7) are calculated using the parametric method of the theory of vibronic spectra of such molecules. Good agreement is obtained between the calculated and experimental spectra. It is shown that the system of parameters of the method for the polyenes has a high degree of transferability in the series of related polyenes. The constructed models adequately reflect the real structure of the molecules in excited states and allow one to predict quantitatively the fine vibrational structure of the spectra, including relatively weak effects related to the methyl substitution. The dynamic of structural changes of the molecules upon their excitation is studied in the series of polyenes.

Optical absorption measurements of silica containing Si nanocrystals produced by ion implantation and thermal annealing

Optical absorption spectra from silicon-implanted silica slides are shown to contain features due to optical interference. These features, which result from the modified refractive index profile produced by the implant, can readily lead to misinterpretation of absorption spectra. To demonstrate the importance of such effects, silica samples were implanted with 80, 400, and 600 keV Si ions to fluences in the range 0.6–3.0×1017 Si.cm−2 and annealed at 1100 °C for 1 h to form Si nanocrystals. Optical absorption/transmittance spectra from these samples show considerable structure that is characteristic of the particular implant conditions. This structure is shown to correlate with the transmittance of the samples as calculated from the modified refractive index profile for each implant. The lack of such structure in absorption spectra measured by photodeflection spectrometry is used to confirm this interpretation.

Identification of structures in absorption spectrum of Kr-Xe gas mixtures close to the Xe resonance line at 146.96 nm

The origins of spectral structures that appear close to the Xe resonance line at 146.96 nm in absorption spectra of Kr gas with an admixture of Xe are discussed in this paper. It is shown that these structures can result from bound-bound and bound-free transitions in the Xe-Kr molecule between the ground state and the 1(3P1) excited state, which both are weakly-bound. The depth of the excited state is estimated. An introduction of a hump on the 1(3P1) state internuclear potential is suggested.

Effect of metal clusters on the absorption and emission spectra of high-density sodium vapors

The optical absorption spectra of high-density (1016–1019 cm−3) sodium vapors were studied in a broad spectral range (0.35–1.1 μm). The intensity of thermal radiation from sodium vapors was measured in the 2–3 μm wavelength interval. It is established that the effect of metal clusters can account neither for the observed structure of absorption spectra nor for the increased intensity of emission in the near-IR range reported in some works (in particular, for the emission spectra of high-pressure gas-discharge sodium lamps).

Double photoexcitation [2(s,p)4(p,d)] in the Xe-isoelectronic series Cs+, Ba2+, La3+

Using the standard ansatz, the single, strongly dissipated harmonic component of EXAFS in aqueous medium is eliminated from L-shell absorption spectra of Xe-like ions Cs + , Ba 2+ , La 3+ . The remaining structures in the spectra are interpreted as double photoexcitations into [2(s, p)4(p, d)] vacancy states: they are analogous to the corresponding structures in absorption spectra of xenon, their energies agree fully with MCDF energies. Their relative probabilities are found to increase along the isoelectronic series, proportionally to the intensity of the «white line» 2p → 5d. For the first time, and «adiabatic» change of double excitation features is studied

Near-threshold photoionisation theory for diatomic molecules

An integral variant of multichannel quantum defect theory is suggested for studying the near-threshold photoionisation of non-symmetrical molecules of the type XY. The main problem here is to express the dipole transition matrix element through corresponding adiabatic parameters of the e-+XY+ system and to reveal its dependence on the incident photon energy. The resonance structure of absorption spectra near the ionisation threshold is shown to be completely determined by the energy dependence of the partial amplitudes of electron-ion scattering that may be investigated independently. Various limits and special cases which demonstrate peculiarities of the interference structure of absorption spectra as well as the role of different factors in the formation of the line profile are considered.

“Hole-burning spectra”. A new method for obtaining fine structure in absorption spectra of organic molecules

A new method is proposed for obtaining fine structure in broad-band absorption spectra of organic molecules in solid solutions at low temperature. This method is based on the laser burning of a series of narrow gaps in inhomogeneously broadened absorption spectra. A special spectral set-up has been developed for the measurement of the differential spectrum (a “hole-burning spectrum”) of “burnt” and “unburnt” samples. As an example the hole-burning spectrum of Zn-tetraphenylporphine in ethanol has been considered.

Direct observation of split-off exciton and phonon structures in absorption spectrum of silicon : T. Nishimo, M. Takeda and Y. Hamakawa. Solid St. Commun.14, 627 (1974)

Direct observation of split-off exciton and phonon structures in absorption spectrum of silicon : T. Nishimo, M. Takeda and Y. Hamakawa. Solid St. Commun.14, 627 (1974)