Changes In Band Shape Research Articles

Search of “chlorophyll forms” in vivo by non‐linear laser spectroscopy

AbstractInduction of a non‐linearity in the long‐wavelength part of the S0 —S1 absorption band of chlorophyll in vivo by a monochromatic pulse results in a simultaneous band shape change in the whole range of investigation (645 – 680 nm). Such homogeneous broadening behaviour at least for time periods ⩾0.5 ns (pulse duration) does not support the hypothesis of many small sub‐bands representing “chlorophyll forms”. The band shape changes at different excitation intensities indicate two excited state absorptions of antenna chlorophyll.

Simulation of the probe frequency dependence of the resonant inverse Raman band shape: A vibronic approach

The change in the inverse Raman band shape was observed by varying the probe frequency in the vicinity of a single photon resonance with a structured electronic absorption band of rhodamine 640 (a strongly fluorescent molecule). The observed band-shape change could be satisfactorily reproduced only if the effect of vibronic transition was properly taken into account. Simulation of the inverse Raman band shape is useful in obtaining structural information on the excited electronic states of fluorescent molecules.

Oil-shale analysis by CP/MAS- 13C n.m.r. spectroscopy

Solid-state 13C n.m.r. (CP/MAS- 13C n.m.r.) spectroscopy provides a direct method for estimating potential oil yields of oil shale formations. Relative aliphatic resonance areas correlate linearly with oil yield and provide a method for oil yield estimation that obviates the need to determine weight per cent organic carbon for each specimen. This direct measurement is performed using an internal area standard, the carbonyl resonance of N-(2- 13C-propanonyl)- N, N, N-trimethylammonium chloride, to monitor spectrometer sensitivity. Oil shale samples obtained as a function of depth at a site in the Mahogany Zone of the Green River Formation show a near-constant aliphatic carbon fraction, f al ≡ (1− f a ), and a twofold, nonlinear variation in oil yield over the vertical dimension of the sampling. Aliphatic carbon resonance band shape changes among these samples are interpreted qualitatively as reflecting a two component mixture composed of the condensed alicyclic structures which link together to form the kerogen matrix and an n.m.r.-distinct but not necessarily chemically distinct contribution from normal-long chain hydrocarbon residues.

Characterization of the Order/Disorder Transition of Poly‐1‐Methyl Adenylic Acid in Neutral Solution by Raman Difference Spectroscopy

AbstractA detailed analysis of the hypo‐ and hyper‐chromic intensity changes as well as the changes in frequency and band shape in the Raman spectra of poly(m1A) upon melting has been made using a newly developed Raman difference technique. An interpretation of these changes allows us to suggest a structure for the double‐helix of this polymer in neutral solution which resembles that of poly(A) in acid pH. In the helix the backbone geometry is shown to be similar to the C 3 endo or A genus and the existence of a hydrogen bond is inferred from the asymmetric band shape of 1100 cm−1 PO−2 stretching vibration wich is not found either in self‐stacked poly(A) at neutral pH. It is expected that the application of the Raman difference technique will result in a detailed description of conformational features of these important macromolecules which cannot be drawn from the resuits of other optical methods.

Quantitative analyses of calcium-induced spectral changes in extrinsic Cotton effects of cobalt-substituted concanavalin A.

The visible cobalt circular dichroism (CD) of cobalt-substituted concanavalin A (Con A) is highly sensitive to Ca2+-induced conformational changes that occur in the metal binding region. The observed ellipticity is separately resolved into discrete conformational spectra with separate extrinsic bands. The conformational forms of the metal region are further delineated on the basis of their differential spectral response to the competitive removal of metals by ethylene-diaminetetraacetic acid (EDTA). The spectral forms sensitive to the effects of EDTA, cobalt-Con A (CPS, epsilon CPS470 - 215 M-1) and calcium-cobalt-Con A (CaCPS, epsilon CaCPS470 = 141 M-1), exhibit both unique extinctions and band shapes in the 400-500-nm region, as does the fully metalized EDTA-resistant species CaCPR (epsilon CaCPR470 = 54 M-1). Equations describing the time dependence of the observed ellipticity have been derived in terms of the kinetic scheme, CPS + Ca in equilibrium or formed from CaCPS in equilibrium or formed from CaCPR, in which the second equilibrium is slow compared to the first. The above assignments allow a more complete quantitative description of the changes in CD amplitudes and band shapes due to Ca2+ binding and thus facilitate the understanding of ca2+ interactions. Calcium binds to 0.93 Ca2+ site/25 500 Mr in CaCPS with a Kd for Ca2+ = 2.1 x 10(-3) M at pH 5.3 and 25 degrees C. The interaction of Ca2+ with CPS to form CaCPS occurs at two equivalent and noninteracting S2 sites each present on separate subunits of the Con A dimer. Furthermore, the rate constant describing the rate of formation of CaCPR was determined.

The KBr Pellet: A Useful Technique for Obtaining Infrared Spectra of Inorganic Species

The reproducibility of the KBr pelleting technique for inorganic sulfates was assessed using a Fourier transform infrared spectrometer. Day-to-day variation in peak frequencies of selected bands had standard deviations ranging from 0. to 1.5 cm−1. This 1 cm−1 standard deviation was shown to be due to changes in bandshape, probably due to variations in sample preparation from operator to operator. It was concluded that the reproducibility of sulfates in KBr is sufficient to allow the design of computerized spectral matching programs to identify specific sulfate species based on band frequencies and intensities.

The vibrational overtone spectrum of liquid methane in the visible and near infrared: Applications to planetary studies

The strengths of 10 bands in the absorption spectrum of liquid methane betwen 19 400 and 6190 Å have been measured. After a small correction for the polarizability of the liquid is applied, for the purpose of comparison with similar gas phase measurements, it is found that there is no temperature dependence of the band strengths between 95 and 295°K. Changes of band shape with temperature cause the 95°K laboratory spectra to resemble Saturn more than room temperature observations do. Gas phase absorption clearly dominates the liquid in planetary spectra, so liquid methane cannot be detected in the outer Solar System by Earth-based observations.

Vibrational relaxation of hydrogen-bonded species in solution. Il. Analysis of vs(XH) absorption bands

The v s(XH) absorption bands of the following complexes have been recorded in digitised form: phenol (OH)- and phenol (OD)- dioxan in CCl 4; phenol (OH)- and phenol (OD)-acetonitrile in CCl 4; and phenol (OH)-acetonitrile in CDCl 3. All these bands are broad and nearly featureless, and have widths at half height ranging from 75 to 148 cm −1. With one possible exception they appear to be free from Fermi resonances. By least-squares fitting of the theoretical bandshape function derived in part I to the experimental spectra we have been able to estimate the parameters Δ, ω 2, and τ C which characterise the theoretical autocorrelation function, and also to determine the v s(XH) stretching frequency very accurately. In the case of phenol (OD)-dioxan in CCl 4 the discrepancies between the observed and fitted spectra can be entirely attributed to errors of observation. It is found that the Kubo parametér τ C Δ is close to unity in all cases, showing that the v s(XH) bands are subject to partial (but not extreme) motional narrowing. The v σ(XH⋯Y) vibration is always heavily damped and has a broad spectral density. The changes in the spectral profiles produced by deuteration and change of solvent are easily understood in terms of the theory. Deuteration affects the amplitude of modulation, while changing the solvent affects the value of τ C. In either case τ CΔ changes, and the speed of modulation is altered. Since the system is far from the gaussian (slow modulation) limit, the bandshape changes markedly in consequence.

Studies of ion–ion and ion–solvent interactions using far-infrared spectroscopy. Part 3. Comparison of observed spectra with results of simple model calculations

The principal features of the far-infrared spectra of tetra-n-alkylammonium salts in non-polar solvents have been compared with the results of some simple model calculations for the motions of, and interactions between, ion-ion and ion-solvent “aggregates.” It has been shown that the spectral features, and their variation with solute, solvent, temperature and concentration, are consistent with the absorptions arising from ion–ion vibrations, ion aggregate “librational” motions and fluctuating electrical fields due to “effective” dipole-induced interactions. The observed intensities are reproduced for model geometries and effective aggregate dipoles which agree very well with those obtained using dielectric relaxation measurements, and it is concluded that the high degree of ion “clustering” in the solutions leads to severe restrictions on the movement of solute and solvent species. It is also thought likely that some solvent molecules may be trapped within the ion “cluster”. Extension of previous measurements down to concentrations of 0.01 mol dm–3 show no obvious changes in band shape or structure and it seems clear that extensive aggregation occurs even in relatively dilute solutions.

Interference effects in the infrared spectra in polarized light of monoclinic crystals

Interferences due to anharmonic interactions between a broad band and discrete energy states have been observed in the infrared spectra of some carboxylic acid salts. In particular, the spectra in polarized light of the ac face of the monoclinic crystals show continuous changes in frequency and band shape in function of the orientation of the electric vector of the incident light. The theory of these spectral interferences developed by Fano for the electronic transition has been extended to the vibrational case in which polarized light is used and it has been shown that the different line profiles of a same band for different orientations of the electric vector can be reproduced.

Normalized magnetic circular polarization measurements on broad luminescence bands

The measurement of normalized magnetic circular polarization (MCP) spectra of broad emission bands is discussed and details of a sensitive MCP spectrometer are reported. The normalizing technique is illustrated by measurements on the broad edge emission of ZnSe single crystals where small changes in band shape and position are observed.

Linear electroabsorption due to substitutional deep impurities in wurtzite‐type crystals: 1. Theoretical analysis for A → T absorption bands

AbstractA theoretical study is made of the first‐order effects of an external electric field on optical transitions between strongly localized electronic states of isolated substitutional impurities in a wurtzite‐type crystal taking into account the near‐tetrahedral symmetry of these centers. The field effect on optical absorption bands due to A → T type transitions is treated on the basis of the method of moments which is extended to include mixing with the A ground level. The field‐induced changes of the zeroth and first moment (corresponding to changes in transition probability and to the Stark splitting, respectively) are calculated as functions of field and polarization direction. The polarization dependence of the zero‐field moments which is due to the axial part of the impurity potential is also discussed. On the basis of a rigid‐shift approximation a brief semi‐phenomenological treatment is given of the field‐induced changes in band shape.

Spectroscopic and magnetic evidence for multiple-state emission from tris(2,2′-bipyridine) ruthenium (II) sulfate

Spectral changes of the charge-transfer photoluminescence of the title compound between 2 and 10°K have been interpreted in terms of a manifold of emitting states in thermal equilibrium. Analysis of the band shape changes by means of the Boltzmann law yields an energy gap of 10.2 cm −1 in excellent agreement with the value obtained from published decay time measurements. A 75-kG magnetic field on the sample maintained at 1.65°K switches the emission back to that seen at 4.2°K. These results also corroborate the assignment of the lowest two states responsible for the luminescence to A 1 and E symmetry in the group D 3.

Design of Efficient Broadband Varactor Upconverters

This paper describes a design procedure for optimizing the performance of a varactor upconverter microwave power amplifier with respect to maximum pump efficiency; the procedure gives explicit diode and circuit parameters and operating levels. An optimum diode is selected by inclusion of an empirical relation between diode breakdown voltage and cutoff frequency. A fully driven abrupt junction diode is assumed. The bandwidth of an upconverter is limited by the intermediate frequency input circuit which typically has a 3 dB bandwidth of about 10 percent. We describe a method of obtaining broadband operation where the interface between the intermediate frequency source and the varactor diode is mismatched in an optimum way. Analysis shows that the frequency variation in mismatch loss just compensates for the frequency variation in upconverter gain predicted by the Rowe-Manley relations. The design procedure is illustrated by a 300 MHz to 10.960 GHz varactor upconverter built for use in the transmitter of the short hop radio system experiment. A bandwidth of 120 MHz between 1.4 dB points represents a bandwidth of more than 40 percent at the intermediate frequency. An output power of +16 dBm was obtained using a pump power of +20 dBm giving a pump efficiency of 40 percent. The normal input to the driver amplifier is +3 dBm giving an overall gain of +13 dB. The upconverter operates over a temperature range of −40°F to +140°F with only a small change in bandshape and output power.

The behavior of spectral features in the infrared emission from particulate surfaces of various grain sizes

Several inorganic materials are used to illustrate that bands in infrared emission spectra of solids change shape as the particle size of the sample is altered, and that the way in which a particular band changes depends upon the value of its absorption coefficient. The relationship found to exist between corresponding band shape changes in emission and reflection spectra indicates that Kirchoff's law holds to a first-order approximation for particulate, or mat, surfaces. The implications of band shape changes are discussed in relation to remote compositional sensing, and it is pointed out as a consequence that the most obvious spectral features used for the identification of samples with polished surfaces are not necessarily the most useful for determining the composition of a target with a rough or mat surface.

Line Shape of the OD Absorption in the Infrared Spectrum of Partially Deuterated Water

SHARP OH bands have recently been reported in partially deuterated solid alcohols which have been attributed to the absence of intermolecular coupling1. We wish to call attention to the remarkable change in band shape for the uncoupled OD oscillator of HDO in H2O on freezing. We have measured the infrared absorption of the OD band near 2,500 cm−1 in dilute solutions of D2O in H2O in conditions where the wings of the band can be observed for at least 250 cm−1 on either side of the absorption maximum. The spectra were digitally recorded and band shapes subjected to numerical analysis. The OD band of ice is sharp (31 cm−1 wide at half-peak height) and Lorentzian for at least twelve half-widths and exhibits no asymmetry in this range. With melting, the band broadens (half-width of 150 cm−1) and is Gaussian in shape for two half-widths. At 4° C no asymmetry is seen; however, at higher temperatures asymmetry appears on the low frequency side of the band. Our high temperature data appear to be in good agreement with those of Falk and Ford2.

K X-Ray emission spectra from silicon and silicon compounds

Wavelength and intensities are reported for the Si K series from silicon metal using primary excitation. Included in the tabulation are the diagram lines α 1,2 and β and the non-diagram or satellite lines α′, α 3, α 4, α 5, α 6, β″ and β‴. The strongest Si K lines (α 1,2, α 3, α 4, β′ and β) are listed for SiO 2 and changes in intensity, wavelength and band shape are discussed. Features of spectra from silicon compounds are shown and compared to results obtained on Al K spectra from aluminum compounds.

Absolute Infrared Intensity Measurements in Thin Films. II. Solids Deposited on Halide Plates

When a thin film of an absorbing substance is deposited on a halide plate, because of various reflection effects, the absorption coefficient measured experimentally in transmission will not correspond to the true absorption coefficient. This paper examines the relationship between this apparent absorption coefficient (α′) and the true absorption coefficient (α). Starting with a rigorous expression for the observed transmission, a relationship is established between α′ and α expressed as an infinite series in powers of d/λ (film thickness divided by wavelength). The result is valid for small d/λ. In the limit as d→0, a very simple relationship connects α and α′. For finite (but not too large) d, higher-order correction terms are derived. The theory is applied to the data of Wieder and Dows on SF6(s) deposited on AgCl and to the data of Yamada and Person on CS2(s) deposited on AgCl. For comparison and to calculate the higher-order correction terms, the data are also fit and analyzed using the damped oscillator model (DOM). The DOM results agree well with the theory. A marked change in band shape due to reflection effects is predicted for the two SF6 fundamentals. Some general suggestions are made concerning experimental procedures. It seems likely that the methods developed in this work will permit reliable corrections for reflection effects in thin film absorption measurements. In the final section, a rigorous method of treating the entire problem is outlined which is applicable, in principle, in all cases. This method depends on the fact that the transmission and phase shift can be related by a Kramers—Kronig-type dispersion relation. It is thus possible, in principle, to calculate α (and the refractive index) under any circumstances without any reference to a physical model. A preliminary application of this method to the SF6 data is presented.

The effects of pressure on the buoyant behavior of deoxyribonucleic acid and tobacco mosaic virus in a density gradient at equilibrium in the ultracentrifuge.

In the original analysis' of the behavior of macromolecules and viruses in a buoyant density gradient at equilibrium in the ultracentrifuge, all components were assumed to be incompressible. As a few hundred atmospheres are normally generated in the liquid, it is to be expected that previous results based on the assumption of incompressibility require re-examination. Several consequences arise on consideration of previously ignored pressuredependent terms. It is shown below that these may be separately considered. (a) There is a redistribution of solute with respect to solvent in the binary medium. (b) The solution is compressed with no change in molality in each of the thin layers perpendicular to the centrifugal field in the liquid column. This compression adds a compression density gradient to the composition density gradient. (c) The banding macromolecular species is compressed and moves to a new neutrally buoyant solution. A change in band shape occurs. It is shown in the analysis below that changes in salt molality in response to pressure are small and may be neglected. The combined effects of compressing the solution and the macromolecular species are significant and affect the band shape, band position, and buoyant density. Theory.-Although the effects of pressure in two- and multicomponent sedimentation equilibrium experiments2-4 have been considered by previous workers, the problem is examined here with special reference to the formation of the density gradient and the behavior of neutrally buoyant macromolecules. For a twocomponent system at equilibrium in a centrifugal field at constant temperature, the thermodynamic relation,