Gas-Phase Electronic Transitions of Carbon Chain Anions Coinciding with Diffuse Interstellar Bands

1998 ◽  
Vol 506 (1) ◽  
pp. L69-L73 ◽  
Author(s):  
M. Tulej ◽  
D. A. Kirkwood ◽  
M. Pachkov ◽  
J. P. Maier
Keyword(s):  
Gas Phase ◽  
Carbon Chain ◽  
Electronic Transitions ◽  
Diffuse Interstellar Bands

scholarly journals Laboratory Electronic Spectra of Carbon Chains and Rings

2013 ◽  
Vol 9 (S297) ◽  
pp. 237-246 ◽  
Author(s):  
L. N. Zack ◽  
J. P. Maier
Keyword(s):  
Gas Phase ◽  
Electronic Spectra ◽  
Multiphoton Ionization ◽  
Ion Trapping ◽  
Electronic Transitions ◽  
Cavity Ringdown Spectroscopy ◽  
Cavity Ringdown ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Optical Wavelengths

AbstractCarriers of the diffuse interstellar bands (DIBs) cannot be definitively identified without laboratory spectra. Several techniques, including matrix isolation, cavity ringdown spectroscopy, resonance enhanced multiphoton ionization, and ion trapping, have been used to measure the electronic spectra of carbon chains and their derivatives. The gas-phase laboratory spectra could then be compared to the astronomical data of known DIBs. The choice of molecules studied in the gas phase depends on the presence of strong electronic transitions at optical wavelengths, the lifetimes of excited electronic states, and chemical feasibility in diffuse astrophysical environments. Collisional-radiative rate models have also be used in conjunction with laboratory spectra to predict absorption profiles under interstellar conditions.

Electronic spectroscopy of the nonlinear carbon chains C4H4+ and C8H4+

2004 ◽  
Vol 82 (6) ◽  
pp. 848-853 ◽  
Author(s):  
Mitsunori Araki ◽  
Pawel Cias ◽  
Alexey Denisov ◽  
Jan Fulara ◽  
John P Maier
Keyword(s):  
Gas Phase ◽  
Electronic Transition ◽  
Electronic Spectroscopy ◽  
Carbon Chain ◽  
Cavity Ringdown Spectroscopy ◽  
Cavity Ringdown ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Phase Spectra ◽  
Electronic Transition Energies

The electronic spectrum of a nonlinear carbon chain radical C4H4+ was observed after mass-selective deposition in a 6 K neon matrix. The corresponding gas-phase spectra of C4H4+ and C4D4+ have been observed in the 512 to 513 nm region and at 710 nm for C8H4+. These were detected in direct absorption by cavity ringdown spectroscopy through a supersonic planar discharge. The electronic transition energies of these nonlinear carbon chain radicals correlate well with those of the polyacetylene cations HCnH+ (n = 4, 6, 8). The observed profiles are reproduced with rotational constants obtained by ab initio geometry optimizations and extrapolation between the ground and excited electronic states. Key words: nonlinear carbon chain, carbon cation, electronic transition, diffuse interstellar bands, molecular structure.

The experimental electronic and vibrational spectra of fulvene

1970 ◽  
Vol 23 (9) ◽  
pp. 1707 ◽  
Author(s):  
RD Brown ◽  
PJ Domaille ◽  
JE Kent
Keyword(s):  
Absorption Spectrum ◽  
Fine Structure ◽  
Gas Phase ◽  
Energy Transition ◽  
Liquid Nitrogen Temperature ◽  
Electronic Transitions ◽  
Mo Calculations ◽  
Polycrystalline Layer ◽  
Partial Analysis ◽  
Electronic And Vibrational Spectra

The infrared spectrum of fulvene has been observed from 250 to 4000 cm-1 in the gas phase, and as a glass and a polycrystalline layer at liquid nitrogen temperature. On the basis of gas-phase contours and P-R separations 14 of the 30 fundamental vibrations have been assigned. The electronic absorption spectrum of fulvene has been recorded from 400 to 167 nm in the gas phase and four electronic transitions have been identified. The lowest-energy transition was found to be broad and structureless while the three higher-energy transitions showed an extensive vibrational fine structure. The electronic transitions have been tentatively assigned on the basis of VESCF-MO calculations and a partial analysis of the vibronic structure has bees made.

scholarly journals Formation, Evolution and Destruction of Possible DIB Carriers: Dirty Molecular Hydrogen Ice Clusters

2013 ◽  
Vol 9 (S297) ◽  
pp. 381-382
Author(s):  
D. K. Lynch ◽  
L. S. Bernstein ◽  
F. O. Clark
Keyword(s):  
Interstellar Medium ◽  
Single Molecule ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Single Layer ◽  
Molecular Clusters ◽  
Electronic Transitions ◽  
Giant Molecular Clouds ◽  
Diffuse Interstellar Bands ◽  
Optical Photons

AbstractWe suggest that the diffuse interstellar bands (DIBs) are absorption lines arising from electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion (“seed”), embedded in a single-layer shell of H2 molecules (Bernstein et al. 2013). We refer to these clusters as CHCs (Contaminated H2 Clusters). CHCs arise from cm-sized, dirty H2 ice balls, called CHIMPs (Contaminated H2 Ice Macro-Particles), formed in cold, dense, Giant Molecular Clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Absorption by the CHIMP of a UV photon releases CHCs. CHCs produce DIBs when they absorb optical photons. When this occurs, the absorbed photon energy disrupts the CHC.

scholarly journals Routes involving no free C2 in a DFT-computed mechanistic model for the reported room-temperature chemical synthesis of C2.

2021 ◽  
Author(s):  
Henry Rzepa
Keyword(s):  
Chemical Synthesis ◽  
Gas Phase ◽  
Room Temperature ◽  
Mechanistic Model ◽  
Reaction Times ◽  
Carbon Chain ◽  
Isotopic Substitution ◽  
Ambient Temperatures ◽  
Mild Conditions ◽  
Displacement Reactions

<p>Recent lively debates about the nature of the quadruple bonding in the diatomic species C<sub>2</sub> have been heightened by recent suggestions of molecules in which carbon may be similarly bonded to other elements. The desirability of having methods for generating such species at ambient temperatures and in solution in order to study their properties may have been realized by a recent report of the first chemical synthesis of free C<sub>2</sub> itself under mild conditions. The method involved unimolecular fragmentation of an alkynyl zwitterion<b> 2</b> as generated from the precursor <b>1</b>, resulting in production and then trapping of free C<sub>2</sub> at ambient temperatures rather than the high temperature gas phase methods normally employed for C<sub>2</sub> generation. Here, alternative mechanisms are proposed for this reaction based on DFT calculations involving bimolecular 1,1- or 1,2-iodobenzene displacement reactions from <b>2</b> directly by galvinoxyl radical, or hydride transfer from 9,10-dihydroanthracene to <b>2</b>. These mechanisms result in the same trapped products as observed experimentally, but unlike that involving unimolecular generation of free C<sub>2</sub>, exhibit calculated free energy barriers commensurate with the reaction times observed at room temperatures. The relative energies of the transition states for 1,1 <i>vs</i> 1,2 substitution provide a rationalisation for the observed isotopic substitution patterns. The same mechanism also provides an energetically facile path to polymeric synthesis of carbon rich species by extending the carbon chain attached to the iodonium group, eventually resulting in formation of amorphous carbon and discrete molecules such as C<sub>60</sub>.</p><div><div><p><br></p></div></div>

scholarly journals Polyacenes and diffuse interstellar bands

2019 ◽  
Vol 625 ◽  
pp. A41 ◽  
Author(s):  
A. Omont ◽  
H. F. Bettinger ◽  
C. Tönshoff
Keyword(s):  
Gas Phase ◽  
Current Knowledge ◽  
Visible Range ◽  
High Symmetry ◽  
Carbon Chains ◽  
Diffuse Interstellar Bands ◽  
Carbon Compounds ◽  
Laboratory Results ◽  
Polycyclic Aromatic ◽  
Recent Laboratory

The identification of the carriers of the diffuse interstellar bands (DIBs) remains to be established, with the exception of five bands attributed to C60+, although it is generally agreed that DIB carriers should be large carbon-based molecules (with ~10–100 atoms) in the gas phase, such as polycyclic aromatic hydrocarbons (PAHs), long carbon chains or fullerenes. The aim of this paper is to investigate more specific possible carriers among PAHs, namely elongated molecules, which could explain a correlation between the DIB wavelength and the apparent UV resilience of their carriers. More specifically, we address the case of polyacenes, C4N+2H2N+4, with N ~ 10–18 fused rectilinear aligned hexagons. Polyacenes are attractive DIB carrier candidates because their high symmetry and large linear size allow them to form regular series of bands in the visible range with strengths larger than most other PAHs, as confirmed by recent laboratory results up to undecacene (C46H26). Those with very strong bands in the DIB spectral domain are just at the limit of stability against UV photodissociation. They are part of the prominent PAH family of interstellar carbon compounds, meaning that only ~10−5 of the total PAH abundance is enough to account for a medium-strength DIB. After summarizing the limited current knowledge about the complex properties of polyacenes and recent laboratory results, the likelihood that they might meet the criteria for being carriers of some DIBs is addressed by reviewing the following properties: wavelength and strength of their series of visible bands; interstellar stability and abundances, charge state and hydrogenation; and DIB rotation profiles. No definite inconsistency has been identified that precludes polyacenes from being the carriers of some DIBs with medium or weak strength, including the so-called C2 DIBs. But, despite their many interesting properties, additional experimental data about long acenes and their visible bands are needed to make robust conclusions.

Computational studies of gas phase reactions of carbon chain anions with N and O atoms

2010 ◽  
Vol 12 (40) ◽  
pp. 13091 ◽  
Author(s):  
Zhibo Yang ◽  
Theodore P. Snow ◽  
Veronica M. Bierbaum
Keyword(s):  
Gas Phase ◽  
Carbon Chain ◽  
Computational Studies ◽  
Gas Phase Reactions
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