UV spectra of iron-doped carbon clusters FeC_n n = 3-6

Electronic transitions of jet-cooled FeC$_n$ clusters ($n = 3 - 6$) were measured between 230 and 300 nm by a mass-resolved 1+1 resonant two-photon ionization technique. Rotational profiles were simulated based on previous calculations of ground state geometries and compared to experimental observations. Reasonable agreement is found for the planar fan-like structure of FeC$_3$. The FeC$_4$ data indicate a shorter distance between the Fe atom and the bent C$_4$ unit of the fan. The transitions are suggested to be $^{3}$A$_{2} \leftarrow ^{3}$B$_{1}$ for FeC$_3$ and $^{5}$A$_{1} \leftarrow ^{5}$A$_{1}$ for FeC$_4$. In contrast to the predicted C$_{\infty \text{v}}$ geometry, non-linear FeC$_5$ is apparently observed. Line width broadening prevents analysis of the FeC$_6$ spectrum.Comment: 6 pages, 5 figure

Electronic spectra of carbon chains and rings: Astrophysical relevance?

Our research has focused on the measurement of the electronic spectra of unstable molecules which are presumed to be of relevance to astrophysical observations. Among these are the carbon chains and their ions. Thus we have been using and developing a number of spectroscopic methods to determine their spectra in the gas phase, including absorption via cavity ring-down and REMPI methods. The species are produced in supersonic jets coupled with discharge and laser ablation sources. With the successful laboratory detection of the electronic spectra of a number of key species, such as bare carbon chains Cn n=4,5, comparisons with astrophysical data could be made which lead to interesting implications for the future search for the species which could be responsible for the diffuse interstellar bands. Among the recent relevant observations in the laboratory have been the electronic spectra of carbon rings, Cn n=14,18,22, the development of a method to study transitions in mass-selected ions collisionally relaxed to 20 K and held in a 22-pole radiofrequency trap, and the study of metal containing carbon chain

Detection of nonpolar lons in 2?3/2 States by Radioastronomy via Magnetic Dipole Transitions

ManuscriptThe possibility of magnetic dipole-induced pure rotational transitions in the interstellar medium is investigated for symmetric Hund?s case (a) linear molecules, such as H-C?C-H+(X~2?3/2u), CO2+ (X~2?3/2g), H-C?C-?C-H+ (X~2?3/2g), and N3 (X~2?3/2g). These species lackan electric dipole moment and therefore cannot undergo pure rotational electric dipole transitions. These species can undergo pure rotational transitions via the parallel component of the magnetic dipole operator, however. The transition moments and Einstein A coefficients for the allowed pure rotational transitions are derived for a general Hund?s case (a) linear molecule, and tabulated for the examples of H-C?C-H+ (2?3/2u) and H-C?C-C?C-H+ (2?3/2g). It is found that the rates of emission are comparable to collision rates in interstellar clouds, suggesting that this decay mechanism may be important in simulating rotational population distributions in diffuse clouds and for detecting these molecules by radioastronomy. Expected line positions for the magnetic dipole-allowed Ref(J) and Rfe(J) transitions of H-C?C-H+ (2?3/2u), H-C?C-C?C-H+ (2?3/2g), CO2 + (2?3/2g), and N3 (2?3/2g) are tabulated to assist in their observation by radioastronomy or in the laboratory

Visible Absorptions of Potential Diffuse ISM Hydrocarbons: C9H9 and C9H5 Radicals

The laboratory detection of previously unobserved resonance-stabilized C9H5 and C9H9 radicals in the supersonic expansion of a hydrocarbon discharge source is reported. The radicals are tentatively assigned as acetylenic-substituted cyclopentadienyl C9H5 and vinyl-substituted benzyl C9H9 species. They are found to feature visible absorption bands that coincide with a few very weak diffuse interstellar bands toward HD183143 and HD204827

Gas phase absorption of C702+ below 10 K: astronomical implications

The electronic spectrum of the fullerene dication C702+ has been measured in the gas phase at low temperature in a cryogenic radiofrequency ion trap. The spectrum consists of a strong origin band at 7030 Å and two weaker features to higher energy. The bands have FWHMs of 35 Å indicating an excited state lifetime on the order of one-tenth of a picosecond. Absorption cross-section measurements yield (2 ± 1) × 10−15 cm2 at 7030 Å. These results are used to predict the depth of diffuse interstellar bands (DIBs) due to the absorption by C702+. At an assumed column density of 2 × 1012 cm−2 the attenuation of starlight at 7030 Å is around 0.4% and thus the detection of such a shallow and broad interstellar band would be difficult. The electronic spectrum of C602+ shows no absorptions in the visible. Below 4000 Å the spectra of C60, C60+ and C602+ are similar. The large intrinsic FWHM of the features in this region, ~200 Å for the band near 3250 Å, make them unsuitable for DIB detection

Electronic Transition of Ferrocenium: Neon Matrix and CASPT2 Studies

Electronic absorptions of ferrocenium starting at 632.5 nm were measured in a 6 K neon matrix following mass-selective deposition of the ions. The spectrum shows clear vibrational structure and provides the best-yet resolved view of the electronic states of this cation. The absorption system is identified as the 1 2E1′ ← X 2E2′ transition (D5h symmmetry) on the basis of vertical excitation energies and oscillator strengths calculated at the CASPT2 level. Vibrational bands in the spectrum are assigned with the aid of the ground-state frequencies calculated with the DFT method

Gas Phase Detection of Benzocyclopropenyl

The gas phase detection of benzocyclopropenyl is reported. In this aromatic resonance stabilized radical, a large angular strain is present due to a three-membered ring annelated to a benzene. The resonant two-color two-photon ionization technique is used to record the D1(2A2) ← D0(2B1) electronic transition of this radical after the in situ synthesis in a discharge source. The spectrum features absorptions up to 3300 cm–1 above the origin band at 19 305 cm–1. Benzocyclopropenyl is possibly the major product of the bimolecular reaction of benzene and an atomic carbon at low temperatures

Experimental Investigation of the Implications of Model Granularity for Design Process Simulation

Determining a suitable level of description, or granularity, for a product or process model is not straightforward, especially since granularity can manifest in multiple ways, but it is important to capture important elements in the model without building models that are too large to understand. This article investigates the implications of model granularity choices by simulating the design process of a diesel engine on different levels of detail, comparing the results and exploring ways to account for the differences. It uses two Design Structure Matrix (DSM) models for change prediction in a diesel engine at different levels of granularity to run simulations of the design process. Changes are a major source of rework and lead to frequent rescheduling of design tasks. The incremental nature of product development as well as design changes and their propagation complicate design process planning further. Process simulation may provide support in such contexts when it is based on an appropriate description of the product. The article shows that while coarse models can give an indication of likely process behavior, they miss potentially significant iteration loops.</jats:p

Electronic Spectrum of Dihydrogenated Buckminsterfullerene in a 6 K Neon Matrix

Vibrationally resolved electronic absorption spectrum of 1,2-dihydrogenated[60]fullerene has been recorded in a 6 K neon matrix after mass-selected deposition of m/z = 722 cations produced from reaction of protonated methane and C60 in an ion source. One system has the origin band at 688.5 ± 0.1 nm and another commencing at 404.8 ± 0.1 nm. Theoretical computations were used to calculate the relative energies of three isomers of dihydrogenated[60]fullerene and time-dependent density functional theory predicted the vertical excitations to 50 electronic states

Electronic spectra of linear HC5_5H and cumulene carbene H2_2C5_5

The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).Comment: 7 pages, 4 figures, 5 table