Unidentified Emission Bands Research Articles

Radiation Effects in Solid Nitrogen

The radiation effects and relaxation processes in pre-irradiated by an electron beam solid $$\hbox {N}_{2}$$ have been studied with a focus on the behavior of the so far unidentified emission band at 360 nm. The study was performed using optical and current spectroscopy methods: cathodoluminescence and developed by our group nonstationary luminescence, as well as spectrally resolved thermally stimulated luminescence, and thermally stimulated exoelectron emission. The measurements cover the temperature range of the $$\alpha $$ -phase existence. Activation spectroscopy evidenced connection of the 360 nm band with the neutralization reaction. Possible scenarios of $$\hbox {N}_{4}^{+}$$ neutralization via dissociative recombination are discussed, and interpretation of the 360 nm band is suggested.

C60 AS A PROBE FOR ASTROPHYSICAL ENVIRONMENTS

ABSTRACT The C60 molecule has been recently detected in a wide range of astrophysical environments through its four active intramolecular vibrational modes (T 1u) near 18.9, 17.4, 8.5, and 7.0 μm. The strengths of the mid-infrared emission bands have been used to infer astrophysical conditions in the fullerene-rich regions. Widely varying values of the relative intrinsic strengths (RIS) of these four bands are reported in laboratory and theoretical papers, which impedes the derivation of the excitation mechanism of C60 in the astrophysical sources. The spectroscopic analysis of the C60 samples produced with our method delivers highly reproducible RIS values of 100, 25 ± 1, 26 ± 1 and 40 ± 4. A comparison of the inferred C60 emission band strengths with the astrophysical data shows that the observed strengths cannot be explained in terms of fluorescent or thermal emission alone. The large range in the observed 17.4 μm/18.9 μm emission ratios indicates that either the emission bands contain significant contributions from emitters other than C60, or that the population distribution among the C60 vibrational modes is affected by physical processes other than thermal or UV excitation, such as chemo-luminescence from nascent C60 or possibly Poincaré fluorescence resulting from an inverse internal energy conversion. We have carefully analyzed the effect of the weakly active fundamental modes and second order modes in the mid-infrared spectrum of C60, and propose that neutral C60 is the carrier of the unidentified emission band at 6.49 μm which has been observed in fullerene-rich environments.

λ4430 Emission by Comet Hyakutake

AbstractComets provide a very different but well understood environment in which to search for DIBs. Observations of occultations by cometary comae have not detected DIBs, but none were very near the nucleus, where the column density of dust is highest. We report here unidentified emission bands, centered at λ4430, very near the nucleus of comet Hyakutake. These may be vaporized forms of grain carriers or fragments of large-molecule carriers. At least two different species appear to be present based on two different spatial distributions.

Theoretical Study on the Ground and Excited States of Dicyanocarbene (C3N2) and Its Isomers: A Low-Temperature Matrix Emission Spectrum Attributable to 3-Cyano-2H-azirenylidene

Ab initio calculations are used to characterize the ground and low lying excited electronic states of selected dicyanocarbene (C(3)N(2) or C(CN)2) isomers. Our calculated ground state geometries and the corresponding vibrational frequencies agree well with available experimental and theoretical data, thereby providing the reliability of the predicted quantities. The present calculations are used to identify the possible emitting species for some unidentified emission bands observed in certain low-temperature matrices. It is found that the 1(3)A' --> X(1)A' transition of 3-cyano-2H-azirenylidene, that is, cyclic C(2)N-CN (Figure 1c) satisfactorily explains all of the observed spectral features of these bands.

Infrared Emission from the CF3+ NO2Reaction

The reaction of the CF3 radical with NO2 has been investigated by using time-resolved FTIR emission spectroscopy. Strong infrared emission has been attributed to products, CF2O and FNO, excited in the ν2 and ν1 modes, respectively. The direct one-step production pathway 1a is suggested as a major reaction channel: CF3 + NO2 → CF2O + FNO, ΔH°298 = −267 kJ mol-1 (1a); → CF2O + F + NO, ΔH°298 = −31 kJ mol-1 (1b). The rate constant for reaction 1 was measured to be (2.4 ± 0.5) × 10-11 cm3 molecule-1 s-1. The F atom formation pathway 1b is the minor channel: the relative branching ratio of reactions 1a and 1b was estimated as 1 : 0.015. The formation of the FON isomer formed via a five-center intermediate is discussed as a possible carrier of an unidentified emission band near 1880 cm-1. The CF3O + NO reaction was investigated by the same technique. Lower emission intensities from the same reaction products were observed, with proportionally less vibrational excitation in the CF2O product.

Molecular Diffuse Interstellar Band Carriers in the Red Rectangle

High-resolution optical spectroscopic observations of unidentified emission bands from the unusual biconical nebula known as the Red Rectangle are reported. The peak wavelengths and the widths of prominent bands near 5799, 5853, and 6616 angstroms decrease with increasing offset from the central A0-type star HD 44179 and, in the limit of large distance from the star, are shown to converge toward the known values for some of the narrower diffuse interstellar absorption bands at 5797, 5850, and 6614 angstroms. The same carriers give rise to both Red Rectangle emission and corresponding diffuse interstellar absorption bands, and these particular bands arise from electronic transitions in gas-phase molecules.

Laser-induced photofragment emission spectrum of vapor phase triethylgallium using 193 nm excitation

The laser-induced photofragment emission (LIPE) spectrum of vapor phase triethylgallium has been obtained using 193 nm excimer laser excitation. Emission lines of C 2, CH and atomic Ga have been identified. An unidentified emission band consisting of regularly spaced peaks near the 450–550 nm region is also observed.

Unusual infrared line profiles in the post-asymptotic giant branch star HD 56126

view Abstract Citations (31) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Unusual Infrared Line Profiles in the Post--Asymptotic Giant Branch Star HD 56126 Kwok, S. ; Hrivnak, Bruce J. ; Geballe, T. R. Abstract Brackett series lines with very broad inverted P Cygni and shell-like profiles have been detected toward the post-AGB star HD 56126. These profiles suggest that an active phase of mass loss has begun recently in this star. The star has had at least one previous episode of intense mass loss, attested to by its strong far-infrared emission. HD 56126 is also known for having a broad emission feature at 21 microns. The unidentified emission bands at 3.3 and 3.4 microns are also present in the spectrum of HD 56126, but the near-infrared spectrum provides little help in establishing the carrier of the 21 microns band. Publication: The Astrophysical Journal Pub Date: September 1990 DOI: 10.1086/185803 Bibcode: 1990ApJ...360L..23K Keywords: Asymptotic Giant Branch Stars; Infrared Sources (Astronomy); Infrared Spectra; Planetary Nebulae; Stellar Evolution; Emission Spectra; Hydrogen; Red Shift; Spectral Energy Distribution; Stellar Spectrophotometry; Astrophysics; INFRARED: SOURCES; NEBULAE: PLANETARY; STARS: CIRCUMSTELLAR SHELLS; STARS: EVOLUTION full text sources ADS | data products SIMBAD (1)

IRSPEC observations of planetary nebulae

We have obtained infrared spectra of planetary nebulae in the 3.0–3.8 μm range using IRSPEC, the ESO grating infrared spectrograph, attached to the 3.6-m telescope. We find evidence of an evolution of the carriers of the unidentified emission bands in the 3 μm region, and explain the observed behaviour in terms of ion irradiation from fast stellar wind.

Observations of Infrared Emission from Galaxies

Aspects of the infrared emission from galaxies obtained from ground-based observations are described. There are clear differences between the dust in galaxies with active nuclei and those dominated by nuclear HII regions. In particular the family of unidentified emission bands between 3 and 13 μm dominate the spectra in the latter objects, but are rarely evident in spectra of active nuclei. However results from spatial, spectral and polarization measurements show that many of the dust properties in galaxies are broadly similar to those in the Milky Way.

Infrared spectrum of the laboratory-synthesized quenched carbonaceous composite (QCC) - Comparison with the infrared unidentified emission bands

Spectre IR de 2,5 a 25 μm de composes carbonaces eteints synthetises, candidats a la «bosse» d'extinction interstellaire a 220 nm

Reexamination of the vacuum ultraviolet emission spectrum of CO in the 950–1200 Å region

New spectrograms of CO below 1200 Å reveal that emission bands terminating on the high energy E 0 1 Σ + and 1Π states plus most of the previously reported unidentified emission bands of CO actually originate from molecular nitrogen. Four new emission band systems in CO, tentatively identified as V 1Π- X 1Σ +, W 1Π- X 1Σ +, Y 1Σ +- X 1Σ +, and Z 1Σ +- X 1Σ +, have been observed. The corresponding T v0 ′s are 98917, 102804, 99963, and 105724 cm −1, respectively.

Photoluminescence Studies in Irradiated Si-Doped Gallium Arsenide

In order to reveal the origin of the 1.40–1.42 eV band which is peculiar to Si-doped GaAs, elaborate investigations of photoluminescence spectra in irradiated and heat-treated Si-doped samples were carried out mainly at 77K. All experimental evidences supported the assignment that the band was caused from a complex of Si atom on As site with As vacancy. Unidentified emission bands at 1.305 and 1.44 eV were observed respectively in (Te + Si)-doped samples subject to electron irradiation and Si-doped samples fired in a dissociation As pressure.