Transparent Spectral Region Research Articles

Multiple electromagnetically induced grating in the 85Rb five-level atomic medium

In this work, a multiple electromagnetically induced grating is realized based on multiple electromagnetically induced transparency in the 85Rb five-level atomic medium. We demonstrate that the diffraction pattern of the probe light field is observed at three different frequency regions corresponding to the three transparent spectral regions of the system. The influence of the intensity and frequency of the coupling laser field on the diffraction pattern of the electromagnetically induced grating and its diffraction efficiency is also investigated, which can find the optimal parameters to improve the higher-order diffraction efficiencies. The appearance of the multiple electromagnetically induced grating in multi-level atomic systems can be applied to photonic devices operating with multiple frequency channels.

Colossal Kerr nonlinearity without absorption in a five-level atomic medium

In this work, we present an analytical method to achieve giant Kerr nonlinearity without absorption in a five-level atomic medium. By using iterative perturbation technique on density matrix equations, we have derived the analytical expressions of nonlinear susceptibility and Kerr nonlinear coefficient in the presence of spontaneously generated coherence (SGC) and relative phase between applied laser fields. It shows that, this five-level atomic medium exhibits multiple electromagnetically induced transparency (EIT) at three different frequencies, at the same time, the Kerr nonlinear coefficient is enhanced around three transparent spectral regions; in each such EIT region appears a pair of positive–negative peaks of Kerr nonlinear coefficient. In particular, these nonlinear peaks are moved to the center of the EIT windows via SGC. This means that the Kerr nonlinear coefficient is enhanced with completely suppressed absorption at different transparency frequencies. Furthermore, the magnitude and the sign of the Kerr nonlinear coefficient are easily controlled according to the SGC strength, the coupling laser intensity, and the relative phase between applied laser fields. Such a giant nonlinear medium can be useful for photonic devices working in the resonant frequency region without absorption. As a typical application, this giant Kerr nonlinear material has been applied to an interferometer for the formation of optical bistability, and showed the appearance of OB at the resonant frequency with significantly reduced threshold intensity and OB width.

Effect of Doppler broadening on giant self-Kerr nonlinearity in a five-level ladder-type system

In this paper, we propose an analytical model to study the effect of Doppler broadening on self-Kerr nonlinearity in a five-level ladder-type atomic system. First- and third-order susceptibilities and the self-Kerr nonlinear coefficient are found as the function of temperature and parameters of laser fields. The analytical model is applied to hot $^{85}{\rm Rb}$85Rb and $^{87}{\rm Rb}$87Rb atoms, and it is shown that under the electromagnetically induced transparency (EIT) effect, the self-Kerr nonlinear coefficient is enhanced around three transparent spectral regions. When the temperature of atomic vapor increases (i.e., Doppler width increases), the depth and width of the EIT windows decrease accordingly, and therefore the amplitude of the Kerr nonlinear coefficient decreases significantly. In addition, because the frequency gaps between hyperfine levels of upper excited state ${{5\rm D}_{5/2}}$5D5/2 of $^{85}{\rm Rb}$85Rb atoms are much smaller than those of $^{87}{\rm Rb}$87Rb atoms, the EIT windows as well as the nonlinear dispersion curves for $^{85}{\rm Rb}$85Rb atoms are closer than those for $^{87}{\rm Rb}$87Rb atoms as the Doppler effect presents. The analytical results agree well with the experimental observation when reducing to a three-level atomic system. The analytical model can be used to easily fit the experimental observations of self-Kerr nonlinearity in a five-level atomic system under different temperature conditions and apply to a variety of applications relating to all-optical-switching techniques.

Optical, morphological and durability studies of quaternary chalcogenide Ge-Sb(As)-(S,Te) films

Thin films from two glassy systems of GexSb40-xS50Te10 and GexAs40-xS50Te10, with compositions x = 10, 20 and 27 at. %, were deposited on optical glass substrates by vacuum thermal evaporation of powdered parent chalcogenide glasses. The complex refractive index and dielectric constants of the films are determined by ellipsometry in a wide spectral range of 0.25–30 μm. In the transparent spectral region of 0.6–2.5 μm the refractive index values are within 2.9–2.3 and 3.3–2.4 for the As-contained and Sb-contained films, respectively. From the IR and Raman data analysis the basic chemical and oxygen-related impurity bonds are identified. The films durability properties were established by applying the US Military Standard quality tests. The quality-test-induced-changes in surface morphology were evaluated. The films are relatively stable after quality test treatments, which cause a small degree of densification and surface roughening for Sb-containing films and surface flattening for As-containing ones.

Optical characterisation of III-V alloys grown on Si by spectroscopic ellipsometry

Increased interest in novel substrates for III-V material growth has led to the use of alloy fractions other than those lattice-matched to traditional GaAs and Ge substrates. The optical constants of these materials are generally not available in the literature. We characterise the unconventional alloy fractions used in a GaAsP/SiGe tandem on Si by spectroscopic ellipsometry on specially prepared samples, with consideration of transparent and opaque spectral regions during analysis. Complex indices of refraction for GaAs.84P.16,Ga.59In.41P, and Al.65In.35P are determined. These values allow improvement of the solar cell and will enable future optical modelling and design of this and other devices and materials.

A New Method for Determining the Optical Constants of Highly Transparent Solids.

Highly transparent substrates are of interest for a variety of applications, but it is difficult to measure their optical constants precisely, especially the absorption index in the transparent spectral region. In this paper, a combination technique (DOPTM-EM) using both the double optical pathlength transmission method (DOPTM) and the ellipsometry method (EM) is presented to obtain the optical constants of highly transparent substrates, which overcomes the deficiencies of both the two methods. The EM cannot give accurate result of optical constants when the absorption index is very weak. The DOPTM is suitable to retrieve the weak absorption index; however, two sets of solutions exist for the retrieved refractive index and absorption index, and only one is the true value that needs to be identified. In the DOPTM-EM, the optical constants are measured first by using the EM and set as the initial value in the gradient-based inverse method used in the DOPTM, which ensures only the true optical constants are retrieved. The new method simultaneously obtains the refractive index and the absorption index of highly transparent substrate without relying on the Kramers-Kronig relation. The optical constants of three highly transparent substrates (polycrystalline BaF2, CaF2, and MgF2) were experimentally determined within wavelength range from ultraviolet to infrared regions (0.2-14 µm). The presented method will facilitate the measurement of optical constants for highly transparent materials.

Spectroelectrochemical Study of Iron Porphyrin Nitrosyls in the Presence of Weak Acids

The infrared spectroelectrochemistry of Fe(OEP)(NO) and Fe(OEPone)(NO), where OEP = octaethylporphyrin and OEPone = octaethylporphinone, was studied in the presence of phenol and substituted phenols. THF-d8 was used as the solvent in order to have the widest transparent spectral region. Previous work in our laboratory [1] has shown that the first reduction product, Fe(OEP)(NO)-, was stable on the spectroelectrochemical timescale. Because the first electron is added to a SOMO orbital, the protonated nitrosyl was not reduced at the potential that it was generated, and kinetic evidence has indicated that a second proton can be added, prior to further reduction. Fe(OEP)(NO)- + PhOH → Fe(OEP)(HNO) + PhO- Fe(OEP)(HNO) + PhOH → Fe(OEP)(H2NO)+ + PhO- Previous work has shown that the Fe(OEP)(H2NO)+ is reduced by three electrons at a potential significantly negative of the Fe(OEP)(NO)0/- wave. The FTIR spectroelectrochemical reduction of Fe(OEP)(15NO) in the presence of 4 mM phenol is shown in figure below (the 15N isotope was used because it moved the νNO band for the reduction product away from the residual bands for protonated THF). The spectra showed the disappearance of the νNO band at 1640 cm-1 and the appearance of the νNO band for Fe(OEP)(NO)- at 1420 cm-1. Other bands were observed for the disappearance of phenol and the appearance of phenolate, either generated by the reactions above or by electrolysis. The band at 1343 cm-1 was a porphyrin band for Fe(OEP)(NO)-. If the potential is scanned to more negative potentials, the 1420 and 1343 cm-1 disappeared as the Fe(OEP)(NO)- species was reduced. At this concentration of phenol, no significant reaction was observed between Fe(OEP)(NO)- and PhOH (phenol). At higher concentrations of phenol, reaction of the Fe(OEP)(NO)- species was observed as the 1420 and 1343 cm-1 disappeared. Under these conditions, detailed analysis was difficult because the phenolate bands due to the direct reduction of phenol obscured the spectrum. The catalytic reduction of H+ by the reduced iron nitrosyl was not observed, as has been seen when stronger acids (such as acetic acid) were used as a proton source [2]. In order to observe the reaction more clearly, two important problems needed to be solved in order to obtain good spectroelectrochemical data. First, the direct reduction of phenol/substituted phenols had to be minimized so that their bands did not overwhelm the spectrum. In addition, the analysis of the data was simplified when the changes in phenol/phenolate bands were only related to the reduction of the iron nitrosyl. The direct reduction was minimized by modifying the platinum surface to raise the overpotential for hydrogen ion reduction. Second, as the reaction proceeded, the solution will naturally become more basic as phenolate ion was generated, raising the pH of the solution. This problem was resolved by buffering the solution with phenolate salts so that the phenol/phenolate ratio remains relatively constant during the reaction. This was also an important reason to minimize the direct reduction of phenol at the electrode surface. Under these conditions, the FTIR spectra were clearer and the related N-O vibration and porphyrin modes could be observed. The spectral results will be presented. In order to observe the oxidation state of the porphyrin itself during the reduction, iron porphinones nitrosyls were studied. In the infrared, the νNO and νCO bands could be readily observed and the FTIR study of these complexes in the absence of weak acids has been reported [3]. Reduction of the Fe(OEPone)(NO) caused downshifts in both the νNO and νCO bands. The electronic structures of the reduced iron porphinone nitrosyl species were interpreted from the comparision of the observed infrared bands and DFT calculations. [1] Y. M. Liu and M. D. Ryan, J. Electroanal. Chem.(1994) 368, 209. [2] L. E. Goodrich, S. Roy, E. E. Alp, J. Zhao, M. Y. Hu and N. Lehnert, Inorg. Chem.(2013) 52, 7766. [3] Z. Wei and M. D. Ryan, Inorg. Chem. (2010) 49, 6948. Figure 1

Spectral dependence of the initiation threshold of explosive decomposition in AgN3

Explosion initiation energy threshold of silver azide was studied for different laser radiation wavelengths. Samples were prepared in the form of pellets (pressed powders), thread-like monocrystals and thin plate polycrystals. A special laser complex was used to perform the experiments. It provided multiparameter measuring of different processes in explosive decomposition of samples. These processes are glowing of decomposing sample, glowing from the irradiated area only, sample acoustic response, shape and energy of a laser pulse. The time resolution for all the experiments made 5ns and synchronization accuracy made 10ns.It was found that silver azide demonstrates high sensitivity to laser radiation in its transparent spectral region (1064nm and 532nm). The explosion initiation energy threshold made 4–8mJ/cm2 for both pressed powders with the free surface and for samples with the covered and pressed by a quartz plate surface. Silver azide crystals require approximately 10 times higher energy density to explode. When the samples were acted by UV laser radiation, their sensitivity was from 50 to 500 times lower for the uncovered samples. The covered and pressed samples demonstrated the sensitivity which was close to that for acted by 1064nm laser radiation.Equal sensitivity of samples to laser radiation with different wavelengths testifies to non-photochemical nature of explosion initiation. The results obtained in the experiments can be consistently explained within the limits of the thermal theory of explosion initiation.

Supercontinuum pulse measurement by molecular alignment based cross-correlation frequency resolved optical gating

We demonstrate that complex supercontinuum and few-cycle ultrashort laser pulses can be fully characterized by using a cross-correlation frequency-resolved optical gating with molecular alignment induced birefringence functioned as a gate. The temporal envelope and phase of the broadband supercontinuum pulse are retrieved by the principal component generalized projection algorithm. This technique shows advantages without phase-matching constraint that may limit the measurable spectral bandwidth, experimental robustness in operating through the whole transparent spectral region of the molecular gases, and intensity sensitivity to measure weak pulses which is inherited from the intrinsic linear process in recording the molecular birefringence induced polarization spectroscopy. Experimental measurements of a few-cycle pulse in the visible region of 525-725 nm confirm that the molecular alignment gating supports a full field characterization of the ultrashort pulse around 10 fs in duration.

Product of alaptide synthesis: Determination of the absolute configuration

Alaptide is the active substance of the veterinary dermatological ointment ALAPTID and a potential drug in human medicine. Electronic circular dichroism spectroscopy (ECD), transparent spectral region optical rotation (OR), and ab initio calculations were employed to determine the absolute configuration of alaptide. No X-ray structural data determining the absolute configuration were available. It was not possible to employ vibrational circular dichroism spectroscopy (VCD), because alaptide was not sufficiently soluble in common solvents used in VCD spectroscopy to generate reliable spectra. Both ECD spectra and OR values of alaptide solution were in good agreement with predicted data and determined unambiguously the absolute configuration of alaptide synthesized from ( S)-alanine as being ( S).

Physicochemical and optical properties of glasses in the Ga4Ge21Se50-Sb2Se3 system

This paper reports on the results of an investigation into the concentration behavior of the glass-forming ability, heat resistance, glass transition temperature, density, refractive index, transparent spectral region, and impurity optical absorption of glasses in the Ga4Ge21Se50-Sb2Se3 system. The data obtained indicate that glasses in the Ga4Ge21Se50-Sb2Se3 system with a high Sb2Se3 content are of interest as materials for use in fiber optics.

Determination of Molecular Structure of Bisphenylene Homologues of BINOL-Based Phosphoramidites by Chiroptical Methods

Vibrational (VCD), electronic circular dichroism (ECD), and IR absorption spectra together with transparent spectral region optical rotation (OR) of two derivatives of bisphenylene 1,1'-binaphthyl-based phosphoramidites containing three stereogenic axes were measured and the results were compared with simulated data obtained by ab initio calculations with density functional theory. An excellent agreement between experimental and predicted B3LYP/6-31G** and BPW91/6-31G** VCD spectra enabled the assignment of all VCD bands in the experimental spectra, while the Gibbs free energy of all the conformers allowed the determination of their relative populations. The calculation of ECD spectra showed that CAM-B3LYP/6-311G** provided results superior to those of B3LYP/6-311G**. The theoretical results for the OR at the B3LYP/6-311G** and CAM-B3LYP/6-311G** levels were in good agreement with experimental optical rotations, but exhibited lower sensitivity in determining particular conformers than VCD and ECD. By a careful comparison of experimental VCD, IR, and ECD spectra and OR with calculated data, it was possible to assign the absolute configuration of all three stereogenic axes and to determine the molecular structure of the studied bisphenylene 1,1'-binaphthyl-based phosphoramidites in solution with a high degree of confidence.

Gallium-nitride nanorods serve as subwavelength optical media

GaN-based LEDs and laser diodes have become the devices of choice for optoelectronic applications operating in the shortwavelength range. One of the remaining challenges for improving GaN-based LEDs is to reduce their optical losses, which are caused by the high refractive index of GaN (∼ 2.5).1 To overcome this difficulty, the low optical reflection from low-effectiverefractive-index (low-n) nanorod arrays could be exploited. To date, there have been few reports about light-extraction enhancement using transparent, conductive indium-tin oxide2 and zinc oxide3 nanorod arrays deposited on top of GaN LEDs. But GaN-nanorod arrays have been shown to have the same physical and thermal properties as the bulk GaN crystal, making them suitable and durable for high-power, GaN-based optoelectronic applications. By analyzing the reflectivity interference fringes, we have quantitatively determined that GaN-nanorod arrays behave as low-n transparent media in the entire visible spectra region.4 Moreover, the polarized properties of single GaN nanorods have been demonstrated and studied in detail.5 By measuring linearly polarized photoluminescence (PL) from individual, isolated GaN nanorods with diameters in the subwavelength regime (30–90nm), we are able to present clear experimental evidence for the size dependence of polarization anisotropy. This can resolve the long-standing issue related to the giant luminescence-polarization anisotropy observed from various semiconductor nanorods and nanowires. In our investigations, high-density, vertically aligned (along the wurtzite c-axis) GaN nanorod arrays were grown using a catalyst-free, self-organized method based on plasma-assisted molecular-beam epitaxy (PA-MBE).6 Judging from results of field-emission, scanning-electron microscopy (FE-SEM), both the average rod diameter and nearest-neighbor separation are in the subwavelength regime of visible light. There are two major advantages of using PA-MBE-grown GaN-nanorod arrays. First, the thickness and filling ratio (volume fraction) of the GaNnanorod array can be tuned by controlling the growth parameters. And, the interfaces formed by PA-MBE are very abrupt, allowing for interferometer-type measurements. We observed strong modulations for all nanorod arrays in the reflection spectra measured in the transparentspectral region. This can be attributed to the effects of Fabry-Perot microcavities formed within the nanorod arrays by optically flat air/nanorod and nanorod/substrate interfaces. Figure 1 shows a representative normal-incident reflectivity spectrum in the near-ultraviolet and visible regions of a GaN-nanorod array. Flat and featureless reflectivity spectra can be observed in the opaque region. Strongly modulated reflectivity spectra are measured in the transparent region. Using an analysis technique based on the spectral positions of the reflectivity fringes, we determined the effective refractive index of the GaN-nanorod array (ne f f ): see Figure 1. The important finding in this analysis is that the effective refractive indices of nanorod arrays in the transparent region can be approximated to the entire dispersion relationship of bulk GaN reflective index by multiplying with a constant of ∼0.65. This value also agrees with that obtained for the opaque region using a filling ratio of ∼0.5. Several semiconductor nanowires have giant emission anisotropy, which is highly desirable in a variety of applications such as polarized LEDs and flat-panel displays. J. Wang and colleagues proposed that the phenomenon is caused by the large dielectric contrast between the nanowire and the surrounding environment, as opposed to quantum-confinement effects.7 H. E. Ruda and A. Shik calculated the detailed effects of dielectric confinement for semiconductor nanowires.8 One important conclusion of their study is the prediction of strong size-dependence of emission anisotropy in the subwavelength regime. Therefore, it is critical to study individual, isolated nanorods with a size distribution within that regime. For our work, the GaN nanorod samples for the polarized PL measurements were prepared with a nanomanipulator system installed

Determination of Absolute Configurations of 4-Hydroxyequilenin-Cytosine and -Adenine Adducts by Optical Rotatory Dispersion, Electronic Circular Dichroism, Density Functional Theory Calculations, and Mass Spectrometry

Estrogen components of some hormone replacement formulations have been implicated in the initiation of breast cancer. Some of these formulations contain equine estrogens such as equilin and equilenin that are metabolized to the genotoxic catechol 4-hydroxyequilenin (4-OHEN). Auto-oxidation generates the o-quinone form that reacts with dC and dA in oligodeoxynucleotides to form unusual stable cyclic bulky adducts, with four different stereoisomers identified for each base adduct. The dC and dA adducts have the same unsaturated bicyclo[3.3.1]nonane type linkage site with identical stereochemical characteristics. Stereochemical effects may play an important part in the biological consequences of the formation of 4-OHEN-DNA adducts, and the assignment of the absolute configurations of the stereoisomeric 4-OHEN-dC and -dA adducts is therefore needed to understand structure-function relationships. We used density functional theory (DFT) to compute the specific optical rotations and electronic circular dichroism (ECD) spectra of the four 4-OHEN-C stereoisomers, and the results were compared with experimentally measured optical rotatory dispersion (ORD) and ECD spectra. The predicted ORD curves for the four stereoisomeric base adducts reproduced the shapes and signs of experimental spectra in the transparent spectral region. The stereochemistry of the C3' atom was determined by comparison of the calculated and experimental ORD and ECD spectra, and the stereochemistry of C2' was determined by mass spectrometric methods. Combining the ORD and mass spectrometry data, the absolute configurations of the four 4-OHEN-C and the stereochemically identical -dC adducts have been identified. The molecular architecture of the linkage site at the 4-OHEN-C/A and 4-OHEN-dC/dA is identical, and it is shown that the deoxyribose group does not substantially contribute to the optical activities. The absolute configurations of the 4-OHEN-dA adducts were thus deduced by comparing the experimental ORD with computed ORD values of 4-OHEN-A adducts.

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: The iso‐schizozygane alkaloids isoschizogaline and isoschizogamine

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the concerted application of DFT calculations of VCD, ECD, and OR to the determination of the ACs of the isoschizozygane alkaloid natural products, isoschizogaline, and isochizogamine, whose ACs have not previously been determined. The ACs of naturally occurring (-)-isoschizogaline and (-)-isoschizogamine, are both determined definitively to be 2R, 7R, 20S, 21S.

Crystallization of thin-film Si monitored in real time by in-situ spectroscopic techniques

We have developed optical techniques for real-time, in-situ monitoring of crystallization and epitaxial growth of silicon. Real-time spectroscopic ellipsometry is used for evaluating epitaxial growth during hot-wire CVD (HWCVD) reveals the thickness at which epitaxy fails and amorphous cones start to nucleate. To distinguish the various processes related to solid phase crystallization of amorphous silicon, we employ, instead, an in-situ real-time reflectance spectroscopy technique, which is simpler and less expensive. Here, we demonstrate the sensitivity of reflectivity spectroscopy to key changes in materials properties. By analyzing reflectance in strongly absorbing UV and transparent IR spectral regions, we distinguish and study the: (1) crystallization mode (random crystallization or solid-phase epitaxy); (2) nucleation location (uniformly in bulk, near film-substrate interface, or film surface); and (3) hydrogen effusion prior to crystallization.

Determination of the Absolute Configurations of Natural Products via Density Functional Theory Calculations of Vibrational Circular Dichroism, Electronic Circular Dichroism and Optical Rotation: The Schizozygane Alkaloid Schizozygine

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the first concerted application of DFT calculations of VCD, ECD, and OR to the determination of the AC of a natural product whose AC was previously undetermined. The natural product is the alkaloid schizozygine, isolated from Schizozygia caffaeoides. Comparison of DFT calculations of the VCD, ECD, and OR of schizozygine to experimental data leads, for each chiroptical technique, to the AC 2R,7S,20S,21S for the naturally occurring (+)-schizozygine. Three other alkaloids, schizogaline, schizogamine, and 6,7-dehydro-19beta-hydroxyschizozygine, have also been isolated from S. caffaeoides and shown to have structures closely related to schizozygine. Assuming a common biosynthetic pathway, their ACs are defined by that of schizozygine.

Determination of Absolute Configuration Using Density Functional Theory Calculations of Optical Rotation and Electronic Circular Dichroism: Chiral Alkenes

In principle, the absolute configuration (AC) of a chiral molecule can be deduced from its optical rotation (OR) and/or its electronic circular dichroism (ECD). In practice, this requires reliable methodologies for predicting OR and ECD. The recent application of ab initio time-dependent density functional theory (TDDFT) to the calculation of transparent spectral region OR and ECD has greatly enhanced the reliability with which these phenomena can be predicted. TDDFT calculations of OR and ECD are being increasingly utilized in determining ACs. Nevertheless, such calculations are not perfect, and as a result, ACs determined are not 100% reliable. In this paper, we examine the reliability of the TDDFT methods in the case of chiral alkenes. Sodium d line specific rotations, [alpha]D, are predicted for 26 conformationally rigid alkenes of known AC, ranging in size from 5 to 20 C atoms, and with [alpha]D values in the range of 0-500. The mean absolute deviation of predicted [alpha]D values from experimental values is 28.7. With one exception, beta-pinene, the signs of [alpha]D are correctly predicted. Errors in calculated [alpha]D values are approximately random. Our results define a "zone of indeterminacy" within which calculated [alpha]D values cannot be used to determine ACs with >95% confidence. TDDFT ECD spectra are predicted for eight of the alkenes and compared to experimental spectra. Agreement ranges from modestly good to poor, leading to the conclusion that TDDFT calculations of ECD spectra are not yet of sufficient accuracy to routinely provide highly reliable ACs. TDDFT OR calculations for two conformationally flexible alkenes, 3-tert-butylcyclohexene and trans-4-carene, are also reported. For the former, predicted rotations are incorrect in sign over the range 589-365 nm. It is possible that the AC of this molecule has been incorrectly assigned.

Measuring the thickness of organic/polymer/biological films on glass substrates using spectroscopic ellipsometry

In this work we discuss a method of determining film thickness for film/substrate combination where the index of refraction of the film and substrate in the transparent spectral regions is almost identical. Common examples of this situation are organic/polymer/biological films on glass substrates. Infrared ellipsometry is used and we use weight gain to provide some necessary additional information for determining the optical functions for the film material. The spectral regions of strong molecular vibrations are then used for determining film thickness.

Determination of Absolute Configuration Using Density Functional Theory Calculation of Optical Rotation: Chiral Alkanes

The recently developed Gauge-Invariant (Including) Atomic Orbital (GIAO) based Time-Dependent Density Functional Theory (TDDFT) methodology for the calculation of transparent spectral region optical rotations of chiral molecules provides a new approach to the determination of absolute configurations. Here, we discuss the application of the TDDFT/GIAO methodology to chiral alkanes. We report B3LYP/aug-cc-pVDZ calculations of the specific rotations of the 22 chiral alkanes, 2-23, of well-established Absolute Configuration. The average absolute deviation of calculated and experimental [alpha](D) values for molecules 2-22 is 24.8. In two of the molecules 2-23, trans-pinane, 10, and endo-isocamphane, 13, the sign of [alpha](D) is incorrectly predicted. Our results demonstrate that absolute configurations of alkanes can be reliably assigned by using B3LYP/aug-cc-pVDZ TDDFT/GIAO calculations if, but only if, [alpha](D) is significantly greater than 25. In the case of (-)-anti-trans-anti-trans-anti-trans-perhydrotriphenylene, 1, [alpha](D) is -93 and TDDFT/GIAO calculations reliably lead to the absolute configuration R(-).