Unusual Spectroscopic Features Research Articles

Peculiar Spectral Evolution of the Type I Supernova 2019eix: A Possible Double Detonation from a Helium Shell on a Sub-Chandrasekhar-mass White Dwarf

We present photometric and spectroscopic data for the nearby Type I supernova (SN Ia) 2019eix (originally classified as an SN Ic), from the day of its discovery up to 100 days after maximum brightness. Before maximum light, SN 2019eix resembles a typical SN Ic, albeit lacking the usual O i feature. Its light curve is similar to the typical SN Ic with decline rates (ΔM 15,V = 0.84) and absolute magnitude M V = −18.35. However, after maximum light, this SN has unusual spectroscopic features, a large degree of line blending, significant line blanketing in the blue (λ < 5000 Å), and strong Ca ii absorption features during and after peak brightness. These unusual spectral features are similar to models of subluminous thermonuclear explosions, specifically double-detonation models of SNe Ia. Photometrically, SN 2019eix appears to be somewhat brighter with slower decline rates than other double-detonation candidates. We modeled the spectra using the radiative-transfer code TARDIS using SN 1994I (an SN Ic) as a base model to see whether we could reproduce the unusual features of SN 2019eix and found them to be consistent with the exception of the O i feature. We also compared SN 2019eix with double-detonation models and found them to best match the observations of SN 2019eix, but failed to reproduce its full photometric and spectroscopic evolution.

Effects of Cr3+ ion concentration on the spectral characterization in Cr3+:Ca0.93Mg1.07Si2O6 crystals

Abstract Four Cr3+:Ca0.93Mg1.07Si2O6 crystals with Cr concentrations in the range of 0.3–2.0 at. % were successfully grown by Czochralski technique. The structure of the crystal was determined by the single-crystal X-ray diffraction method. The absorption spectra, fluorescence spectra and fluorescence decay curve were measured. There are two broad absorption bands with peaks at around 446 nm and 650 nm, respectively. With the increasing of the Cr3+ ions concentrations in the crystals, the fluorescence spectra showed a large redshift, with the emission peaks shifted from 783 nm to 986 nm. It is found that the two crystallographic Mg sites in the structure lead to the two different emission bands. The crystal field splitting (Dq), Racah parameters Dq/B and the decay curves were analyzed to distinguish the origins of the two peaks. The results show that the Cr3+:Ca0.93Mg1.07Si2O6 crystals have unusual spectroscopic features and may have a potential application for tunable and ultrashort lasers.

Raman Scattering in Carbon Nanosystems: Solving Polyacetylene.

Polyacetylene has been a paradigm conjugated organic conductor since well before other conjugated carbon systems such as nanotubes and graphene became front and center. It is widely acknowledged that Raman spectroscopy of these systems is extremely important to characterize them and understand their internal quantum behavior. Here we show, for the first time, what information the Raman spectrum of polyacetylene contains, by solving the 35-year-old mystery of its spectrum. Our methods have immediate and clear implications for other conjugated carbon systems. By relaxing the nearly universal approximation of ignoring the nuclear coordinate dependence of the transition moment (Condon approximation), we find the reasons for its unusual spectroscopic features. When the Kramers–Heisenberg–Dirac Raman scattering theory is fully applied, incorporating this nuclear coordinate dependence, and also the energy and momentum dependence of the electronic and phonon band structure, then unusual line shapes, growth, and dispersion of the bands are explained and very well matched by theory.

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study

The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40,000 cm(-1) are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ˙(+) exhibits a very conspicuous and complicated pattern of features above 1900 cm(-1) that is due to this electronic transition, and offers an unusually vivid demonstration of the effects of vibronic coupling in what would usually be a relatively simple region of the electromagnetic spectrum associated only with vibrational transitions. As expected, the intensities of most of the IR transitions leading to levels that couple the ground to the very low-lying first excited state of PBQ˙(+) increase by large factors upon ionization, due to "intensity borrowing" from the D0 → D1 electronic transition. A notable exception is the antisymmetric C=O stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

A DFT investigation of structure and spectroscopic properties of haplophytine and its half-molecules

The natural product haplophytine and its half-molecules, aspidophytine and the still elusive ‘left domain’, exhibit unique structural skeletons and unusual spectroscopic features. These issues have been tackled with density functional calculations. The congested framework of haplophytine consists of two heteropolycyclic segments connected with a sterically demanding single bond and incorporates two protonation sites of different basicity and a relatively strong hydrogen bond O–H⋯O, responsible for the acidic activity. The molecular and electronic structure of these alkaloids has been elucidated by analysing the carbonyl vibrations, 13C NMR chemical shifts, and UV absorption spectra that are most sensitive to stereoelectronic factors.

An Unusually Fast-Evolving Supernova

Analyses of supernovae (SNe) have revealed two main types of progenitors: exploding white dwarfs and collapsing massive stars. Here we describe SN 2002bj, which stands out as different from any SN reported to date. Its light curve rose and declined very rapidly, yet reached a peak intrinsic brightness greater than -18 magnitude. A spectrum obtained 7 days after discovery shows the presence of helium and intermediate-mass elements, yet no clear hydrogen or iron-peak elements. The spectrum only barely resembles that of a type Ia SN, with added carbon and helium. Its properties suggest that SN 2002bj may be representative of a class of progenitors that previously has been only hypothesized: a helium detonation on a white dwarf, ejecting a small envelope of material. New surveys should find many such objects, despite their scarcity.

N2O Reduction by the μ4‐Sulfide‐Bridged Tetranuclear Cuz Cluster Active Site.

AbstractFor Abstract see ChemInform Abstract in Full Text.

N2O reduction by the mu4-sulfide-bridged tetranuclear CuZ cluster active site.

Nitrous oxide (N2O) reduction is a chemical challenge both in the selective oxidation of organic substrates by N2O and in the removal of N2O as a green-house gas. The reduction of N2O is thermodynamically favorable but kinetically inert, and requires activating transition-metal centers. In biological systems, N2O reduction is the last step in the denitrification process of the bacterial nitrogen cycle and is accomplished by the enzyme nitrous oxide reductase, whose active site consists of a micro4-sulfide-bridged tetranuclear CuZ cluster which has many unusual spectroscopic features. Recent studies have developed a detailed electronic-structure description of the resting CuZ cluster, determined its catalytically relevant state, and provided insight into the role of this tetranuclear copper cluster in N2O activation and reduction.

Modern Screening Techniques for Plant Extracts

In order to discover new bioactive compounds from plantsources which could become new leads or new drugs, extractsshould be simultaneously evaluated by chemical screeningand by various biological or pharmacological targets. Chemicalscreening using hyphenated techniques such as LC/UVand LC/MS, and more recently LC/NMR, quickly providesample structural information, leading in many cases to theidentification of compounds. This allows researchers to distinguishbetween known compounds (dereplication) andnew molecules directly from crude plant extracts. Thus, thetedious isolation of known compounds can be avoided, and atargeted isolation of constituents presenting novel or unusualspectroscopic features can be undertaken. In parallel, extractsare also subjected to various bioassays that should be simple,reproducible, and rapid. This approach will be illustrated bythe search for new molluscicidal, antioxidant, and antifungalcompounds from tropical plants.

Spectroscopic study of Eu 3+ in strontium hydroxyapatite Sr 10(PO 4) 6(OH) 2

The Eu 3+ time-resolved luminescence in the strontium hydroxyapatite Sr 10(PO 4) 6(OH) 2 prepared by solid-state reaction is studied at 20 K. The emission mainly arises from the 5 D 0 level. The study is focused on the distribution of sites which exhibit unusual spectroscopic features as in other apatites due to an Eu–O privileged bonding with Eu 3+ located in (6h) positions. Non-selective UV excitation and the site-selective-laser excitation in the 5 D 0 and 5 D 1 levels were performed. Luminescence decay profiles of the 5 D 0 -europium sites were recorded.

Cis-2,3-Di-tert-butylcyclopropanones

The preparation of the strained cis-2,3-di-tert-butylcyclopropanone 2 from the acyclic compound, α,α′-dibromodineopentyl ketone 1, using a previously reported methodology, is dramatic evidence of both the existence of oxyallyl intermediates in the mechanism of this reaction, and of the integrity with which oxyallyls ring-close to cyclopropanones by a disrotatory route. Because of the bulky cis substituents, cyclopropanone 2 exhibits a number of unusual spectroscopic features (as compared to the trans isomer 5). With the aid of ab initio calculations on 2 and 5, it can be shown that the C2—C3 bond in 2 interacts with the carbonyl π-orbitals, thus causing the carbonyl oxygen to bend 12° out of the plane; this interaction is absent in 5 and the latter has a planar carbonyl group. As with other cyclopropanones, 2 can be photochemically decarbonylated. This process itself appears to be stereospecific even though highly strained alkenes are produced. Cyclopropanone 2 is thermally rearranged to the trans isomer 5 and the kinetics for this are reported; our favoured mechanism involves oxyallyl intermediates. Other reactions of 2 also appear to proceed through these oxyallyl species; for example, alcohols initially add to 2 to give α-alkoxy ends, solutions of 2 enter into very facile diene cycloadditions, and the dimerization of neat 2 also appears to involve these oxyallyl species. Keywords: cyclopropanones, oxyallyl, stereomutation, stereospecific decarbonylation, nonplanar carbonyl.

Silicate crystals for infra-red lasers

This paper reviews the spectroscopic properties of octahedral Cr 3+ and tetrahedral Cr 4+ active centers in silicate crystals of diopside (CaMgSi 2O 6), Sc 2SiO 5, AB4(SiO 4) 3O with A = Ca or Sr and B = Y, Ln, Gd. These crystals demonstrate unusual spectroscopic features and potential for new laser applications.

XPS and EELS study of a quasicrystalline Al 70Pd 20Mn 10 alloy

The electronic structure of an icosahedral Al 70Pd 20Mn 10 quasicrystal has been investigated by X-ray photoelectron and electron energy-loss spectroscopy. The spectral form of the valence band, the core-level intensities and the core-level shifts all strongly indicate a close resemblance to crystalline AlPd. The density of states at the Fermi level of the quasicrystal is found to be significantly lower than that of pure Al, Pd and Mn. XPS spectra show a satellite that accompanies the main Pd lines at 18 eV. The same broad feature is observed in EELS, while plasmon losses characteristic of pure Al are suppressed. Hence, the concentration of nearly-free electrons is significantly low, in agreement with the relatively high resistivity of the material. Other than that, no unusual spectroscopic features are observed that could be attributable to the quasicrystalline structure of the Al 70Pd 20Mn 10 alloy.

Color change and other unusual spectroscopic features predicted by the model of hole superconductivity

The model of hole superconductivity postulates that the mobility of a hole carrier increases with the hole concentration in the system. From this single assumption follows the existence of superconductivity in the system in the regime of low hole concentration, and a number of unusual spectroscopic features: (1) Spectral weight in the frequency-dependent conductivity should be transfered from high to low frequencies in the normal state as the system is doped; (2) A similar spectral weight transfer in the frequency-dependent conductivity should occur for fixed carrier concentration as the temperature is lowered and the system becomes superconducting; (3) In the single-particle density of states, spectral weight transfer between positive and negative energies should occur when the system is cooled below T c, leading to an asymmetry in tunneling and photoemission experiments: an enhanced spectral weight in photoemission and a corresponding decreased spectral weight in inverse photoemission, and a larger tunneling current in a negatively compared to a positively biased sample, should be seen; (4) In angle resolved photoemission the sharpest peaks in the normal and superconducting states should occur for different k-values, and in a range of k-values the peak should move towards the Fermi energy in the superconducting state while it is moving away from it in the normal state.

ChemInform Abstract: Unusual Spectroscopic Features in the Emission and Absorption Spectra of Single‐Crystal K2(PtCl4) Caused by Multiple‐Mode Excited‐State Distortions.

AbstractThe vibronic structure of the luminescence spectrum (regularly spaced vibronic progression of 315 cm‐1) and the energy gap between the emission and absorption spectra are analyzed.

Unusual spectroscopic features in the emission and absorption spectra of single-crystal potassium tetrachloroplatinate(II) (K2[PtCl4]) caused by multiple-mode excited-state distortions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTUnusual spectroscopic features in the emission and absorption spectra of single-crystal potassium tetrachloroplatinate(II) (K2[PtCl4]) caused by multiple-mode excited-state distortionsD. M. Preston, Wolfgang. Guentner, Alfred. Lechner, Guenter. Gliemann, and Jeffrey I. ZinkCite this: J. Am. Chem. Soc. 1988, 110, 17, 5628–5633Publication Date (Print):August 1, 1988Publication History Published online1 May 2002Published inissue 1 August 1988https://doi.org/10.1021/ja00225a007RIGHTS & PERMISSIONSArticle Views157Altmetric-Citations30LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (780 KB) Get e-Alerts Get e-Alerts

The C2H, C2, and CN electronic absorption bands in the carbon star HD 19557

view Abstract Citations (40) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The C2H, C2 and CN electronic absorption bands in the carbon star HD 19557. Goebel, J. H. ; Bregman, J. D. ; Cooper, D. M. ; Goorvitch, D. ; Langhoff, S. R. ; Witteborn, F. C. Abstract Infrared spectrophotometry of the R-type carbon star HD 19557 is presented. Two unusual spectroscopic features are seen: a 3.1 micron band is lacking and a 2.8 micron band is present. Identifications are proposed for three previously unreported stellar absorption bands with electronic sequences of C2, CN, and C2H. The latter is proposed to be responsible for the 2.8 micron feature. The atmospheric structure of the star is studied with synthetic spectra, and an effective temperature between 2600 K and 3000 K is suggested. No SiC emission is seen at 11.3 microns, indicating that grain formation is not a viable process around the star. The lack of dust in R stars may suggest a salient difference between R and N types. Publication: The Astrophysical Journal Pub Date: July 1983 DOI: 10.1086/161110 Bibcode: 1983ApJ...270..190G Keywords: Absorption Spectra; Carbon Stars; Cyanogen; Electronic Spectra; Infrared Astronomy; Stellar Spectrophotometry; Infrared Spectra; Molecular Spectra; Stellar Atmospheres; Astrophysics full text sources ADS | data products SIMBAD (2)

Messung von Oszillatorenstärken im Singulettsystem des neutralen Magnesiums

A novel type of confined arc has been constructed. Its high magnesium density (up to several 1015 cm−3) provides some unusual spectroscopic features. Relativef-values have been measured for the lines 31P-n1D,n=4...9 and 31P-n1S,n=5,6. By separate comparison with the line 33P10-33P2, these values were placed on an absolute scale.