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

Experimentelle und theoretische Untersuchungen zur UV-VIS-Spektroskopie großer astrophysikalisch relevanter Kohlenwasserstoff-Moleküle

Der Ursprung der diffusen interstellaren Banden (DIBs) und des UV-Bumps bei 217.5 nm beschäftigt Astrochemiker inzwischen seit mehr als einem halben Jahrhundert. Von deren Aufklärung verspricht man sich entscheidende Erkenntnisse über die Physik und Chemie der interstellaren Materie. Im Verlaufe dieser Arbeit wurden die elektronischen Absorptionseigenschaften großer, auf dem Element Kohlenstoff basierender Moleküle untersucht, für deren Vorhandensein im interstellaren Medium (ISM) deutliche Hinweise existieren. Unter Anwendung von Laborexperimenten, die die Bedingungen des ISM simulieren, in Kombination mit theoretischen Vorhersagen konnte u.a. gezeigt werden, dass polyzyklische aromatische Kohlenwasserstoffe (PAHs) in neutraler sowie einfach ionisierter Form für den Bump in der Extinktionskurve bei 217.5 nm verantwortlich sein können, wenn sie im Mittel aus etwa 50 (oder mehr) C-Atomen bestehen. Diverse Indizien sprechen jedoch dagegen, dass diese Moleküle, wie vielfach vermutet wird, auch Träger der DIBs sind. Dass Diamantoide, aus mehreren Diamanteinheitszellen aufgebaute Moleküle, auf der Erde natürlich vorkommen, konnte erst vor kurzem nachgewiesen werden. Aufgrund der ebenfalls in dieser Arbeit untersuchten spektroskopischen Eigenschaften dieser Spezies dürfte sich ein Nachweis in astrophysikalischen Objekten anhand spektraler Charakteristika jedoch als schwierig erweisen. Davon ausgenommen könnten die kleinsten Moleküle dieser Art, wie Adamantan (eine Zelle) und Diamantan (zwei Zellen), sein. Anhand elektronischer Signaturen im UV konnte nachgewiesen werden, dass deren Ionisierung, ausgelöst duch Bestrahlung mit FUV-Photonen, wie sie im interstellaren Raum reichlich vorhanden sind, vom gleichzeitigen Verlust eines peripheren H-Atoms begleitet wird. Dadurch bilden sich stabile Ionen mit abgeschlossenen Molekülschalen, die ein permanentes elektrisches Dipolmoment aufweisen und demzufolge mittels radioastronomischer Beobachtungen aufgespürt werden könnten.The most puzzling mystery of modern astrochemistry lies probably behind the absorption bands that are superimposed on the interstellar extinction curve in the visible and ultraviolet spectral range. The origins of the (in)famous diffuse interstellar bands (DIBs) and the UV bump at 217.5 nm bother scientists for more than half a century. The solution of this problem promises key insights into the physics and chemistry of interstellar matter. In the course of this work, the electronic absorption properties of various large carbon-based molecules, for whose existence in the interstellar medium (ISM) distinct hints exist, were investigated. Applying laboratory experiments, aimed at simulating the ISM conditions, in combination with theoretical predictions, based on modern quantum chemical calculations, it was shown that neutral and singly ionized polycyclic aromatic hydrocarbons (PAHs) composed of roughly 50 (or more) C atoms can be responsible for the bump in the extinction curve at 217.5 nm. On the other hand, as suggested by various indications, none of these molecules is probably a carrier of a strong DIB. Quite recently, so-called diamondoids, molecules composed of several faced-fused diamond cages, were found on Earth in natural sources. However, a detection in astrophysical objects through astronomical observations in the UV-vis may be complicated by the particular spectral characteristics of these species as they were uncovered in the present work. Even though, the smallest molecules, like adamantane (1 cage) and diamantane (2 cages), may be found in other wavelength regions. Based on electronic signatures in the UV, it was demonstrated that the ionization caused by an irradiation with FUV photons (as they are amply present in interstellar space) is accompanied by the subsequent loss of a peripheral H atom. As a result, stable closed-shell ions are formed which possess a permanent electric dipole moment and, hence, may be detected via radio-based observations

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 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

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

The abundances of hydrocarbon functional groups in the interstellar medium inferred from laboratory spectra of hydrogenated and methylated polycyclic aromatic hydrocarbons

Infrared (IR) absorption spectra of individual polycyclic aromatic hydrocarbons (PAHs) containing methyl (-CH3), methylene (>CH2), or diamond-like *CH groups and IR spectra of mixtures of methylated and hydrogenated PAHs prepared by gas phase condensation were measured at room temperature (as grains in pellets) and at low temperature (isolated in Ne matrices). In addition, the PAH blends were subjected to an in-depth molecular structure analysis by means of high-performance liquid chromatography, nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Supported by calculations at the density functional theory level, the laboratory results were applied to analyze in detail the aliphatic absorption complex of the diffuse interstellar medium at 3.4 mu-m and to determine the abundances of hydrocarbon functional groups. Assuming that the PAHs are mainly locked in grains, aliphatic CHx groups (x = 1,2,3) would contribute approximately in equal quantities to the 3.4 mu-m feature (N_{CHx} / N_{H} approx 10^{-5} - 2 * 10^{-5}). The abundances, however, may be two to four times lower if a major contribution to the 3.4 mu-m feature comes from molecules in the gas phase. Aromatic =CH groups seem to be almost absent from some lines of sight, but can be nearly as abundant as each of the aliphatic components in other directions (N_{=CH} / N_{H} < 2 * 10^{-5}; upper value for grains). Due to comparatively low binding energies, astronomical IR emission sources do not display such heavy excess hydrogenation. At best, especially in proto-planetary nebulae, >CH2 groups bound to aromatic molecules, i.e., excess hydrogens on the molecular periphery only, can survive the presence of a nearby star.Comment: 34 pages, 19 figures, ApJS, 208, 2

Probing different spin states in xylyl radicals and ions

Resonant one-color two-photon ionization spectroscopy and mass-selected threshold photoelectron spectroscopy were applied to study the electronic doublet states of the three xylyl (methyl-benzyl) radicals above 3.9 eV as well as the singlet and triplet states of the cations up to 10.5 eV.</p

The genetic interactome of prohibitins: coordinated control of cardiolipin and phosphatidylethanolamine by conserved regulators in mitochondria

Prohibitin ring complexes in the mitochondrial inner membrane regulate cell proliferation as well as the dynamics and function of mitochondria. Although prohibitins are essential in higher eukaryotes, prohibitin-deficient yeast cells are viable and exhibit a reduced replicative life span. Here, we define the genetic interactome of prohibitins in yeast using synthetic genetic arrays, and identify 35 genetic interactors of prohibitins (GEP genes) required for cell survival in the absence of prohibitins. Proteins encoded by these genes include members of a conserved protein family, Ups1 and Gep1, which affect the processing of the dynamin-like GTPase Mgm1 and thereby modulate cristae morphogenesis. We show that Ups1 and Gep1 regulate the levels of cardiolipin and phosphatidylethanolamine in mitochondria in a lipid-specific but coordinated manner. Lipid profiling by mass spectrometry of GEP-deficient mitochondria reveals a critical role of cardiolipin and phosphatidylethanolamine for survival of prohibitin-deficient cells. We propose that prohibitins control inner membrane organization and integrity by acting as protein and lipid scaffolds

Electronic Spectroscopy of Resonantly Stabilized Aromatic Radicals : 1-Indanyl and Methyl Substituted Analogues

The gas-phase electronic spectra of two resonantly stabilized radicals, 1-indanyl (C9H9) and 1-methyl-1-indanyl (C10H11), have been recorded in the visible region using a resonant two-color two-photon ionization (R2C2PI) scheme. The D1(A″) ← D0(A″) origin bands of 1-indanyl and 1-methyl-1-indanyl radicals are observed at 21157 and 20565 cm–1, respectively. The excitation of a′ vibrations in the D1 state is observed up to ∼1500 cm–1 above the origin band in both cases. The experimental assignments are in agreement with DFT and TD-DFT calculations. The R2C2PI spectrum recorded at m/z = 131 amu (C10H11) features three additional electronic transitions at 21433, 21369, and 17989 cm–1, which are assigned to the origin bands of 7-methyl-1-indanyl, 2,3,4-trihydronaphthyl, and methyl-4-ethenylbenzyl radicals, respectively

Electronic spectroscopy of resonance-stabilised C6H7 radicals

Electronic spectra of C6H7 radicals, α-hydrofulvenyl and cis/trans-1-vinyl-3-methylpropargyl, have been measured in the gas phase. A resonant two-colour, two-photon ionisation scheme was used after the radicals were produced in a supersonically cooled discharge source. The origin bands in D1 (2A″) ← D0 (2A″) transitions are observed at 18,734, 21,278 and 21,698 cm−1, respectively. The assignment of the spectra is based on the calculated harmonic frequencies in the D1 states and the available literature data