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

Synthesis and Spectroscopy of Buckminsterfullerene Cation C₆₀⁺ in a Cryogenic Ion Trapping Instrument

The assignment of several diffuse interstellar bands in the near-infrared to C60+ ions present at high abundance in space has renewed interest in the astrochemical importance of fullerenes and analogues. Many of the latter have not been produced in macroscopic quantities, and their spectroscopic properties are not available for comparison with astronomical observations. An apparatus has been constructed that combines laser vaporisation synthesis with spectroscopic characterisation at low temperature in a cryogenic trap. This instrument is used here to record the electronic absorptions of C60+ produced by laser vaporisation of graphite. These are detected by (helium tagged) messenger spectroscopy in a cryogenic trap. By comparison with spectra obtained using a sublimed sample of Buckminsterfullerene, the observed data show that this isomer is the dominant C60+ structure tagged with helium at m/z=724, indicating that the adopted approach can be used to access the spectra of other fullerenes and derivatives of astrochemical interest

Electronic Spectroscopy of Monocyclic Carbon Ring Cations for Astrochemical Consideration

[Image: see text] Gas phase electronic spectra of pure carbon cations generated by laser vaporization of graphite in a supersonic jet and cooled to below 10 K and tagged with helium atoms in a cryogenic trap are presented. The measured C(2n)(+)–He with n from 6 to 14, are believed to be monocyclic ring structures and possess an origin band wavelength that shifts linearly with the number of carbon atoms, as recently demonstrated through N(2) tagging by Buntine et al. (J. Chem. Phys.2021, 155, 21430234879679). The set of data presented here further constrains the spectral characteristics inferred for the bare C(2n)(+) ions to facilitate astronomical searches for them in diffuse clouds by absorption spectroscopy

Electronic spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration

Context. Polycyclic aromatic hydrocarbons (PAHs) are believed to be the carriers of the aromatic infrared bands and have been proposed as candidates to explain other astronomical phenomena such as diffuse interstellar bands (DIBs). The first aromatic structures possessing more than one ring, 1- and 2-cyanonaphthalene (CNN), were recently detected by rotational spectroscopy in the dense molecular cloud TMC-1. Laboratory investigations have indicated that due to fast and efficient relaxation through recurrent fluorescence (RF), CNN+ may be photostable in the harsh conditions of the lower density, more diffuse regions of the interstellar medium (ISM) exposed to ultraviolet (UV) radiation. As a result, it has been suggested that the widely held belief that small PAHs present in these regions are dissociated may need to be revisited. If 1-CNN+ is able to survive in the diffuse ISM it may contribute to the population of 1-CNN observed in TMC-1. To investigate the abundance of 1-CNN+ in diffuse clouds, laboratory spectroscopy is required. The present work concerns the electronic spectroscopy of 1-CNN+ in absorption and the search for its spectroscopic fingerprints in diffuse clouds. Aims. The aim is to obtain laboratory data on the electronic transitions of gas-phase 1-CNN+ under conditions appropriate for comparison with DIBs and assess abundance in diffuse clouds. Methods. Spectroscopic experiments are carried out using a cryogenic ion trapping apparatus in which gas-phase 1-CNN+ is cooled to temperatures below 10 K through buffer gas cooling. Calculations are carried out using time-dependent density-functional theory. Results. Experimental and theoretical data on the D2 ← D0 and D3 ← D0 electronic transitions of 1-CNN+ are reported. The former transition has a calculated oscillator strength of f = 0.075 and possesses a pattern dominated by its origin band. The origin band is located at 7343 Å and has a full width at half maximum of 28 Å. In observational data, this falls in a region polluted by telluric water lines, hindering assessment of its abundance. Conclusions. Space-based observations are required to search for the spectroscopic signatures of 1-CNN+ and evaluate the hypothesis that this small aromatic system, stabilised by RF, may be able to survive in regions of the ISM exposed to UV photons

Electronic Spectroscopy of He@C60+ for Astrochemical Consideration

The electronic spectrum of the endohedral fullerene He@C+60 observed by messenger spectroscopy in a cryogenic ion trap is presented. The role played by the messanger tag in the adopted experimental method is evaluated by recording spectra of He@C+60 − Hen with n = 1−4. The results indicate a linear shift of ∼ 0.7 Å in the wavelengths allowing accurate gas phase values to be reported. The presence of the helium inside the cage shifts the absorption bands by 2−3 Å toward shorter wavelengths compared to C+60. The magnitude of this displacement will enable searches for the spectral signatures of this fullerene analogue in interstellar environments by absorption spectroscopy. The implications for potential astronomical detection are discussed

Isomeric and isotopic effects on the electronic spectrum of C60+-He: consequences for astronomical observation of C60+

Laboratory measurements are reported that enable a more accurate determination of the characteristics of the near-infrared absorptions of C-60(+) below 10 K. These data were obtained by photofragmentation of C-60(+)-He complexes in a cryogenic trap. Asymmetry in the profiles of the observed 9577 and 9632 angstrom absorption bands of C-60(+)-He is caused by the attachment of the weakly bound helium atom to hexagonal or pentagonal faces of C-60(+). The implication is that the FWHM of the bands in the electronic spectrum of C-60(+) below 10 K is 1.4 angstrom. The effect of C-13 isotopes on the C-60(+) electronic spectrum is experimentally evaluated by measurement of C-12(60)+-He, (C1C59+)-C-13-C-12-He, and (C2C58+)-C-13-C-12-He. Data on the 9365 angstrom absorption band indicate a wavelength shift of about 0.3 angstrom between the former and latter. This result is consistent with models used to interpret the vibrational isotope effect in the Raman spectrum of neutral C-60. The influence of C-13 isotopes on the 9348, 9365, 9428, 9577, and 9632 angstrom diffuse interstellar bands is expected to be minor considering other broadening factors that affect astronomical observations. The presented data also provide more accurate relative intensities of the five interstellar bands attributed to C-60(+)

Gas-phase electronic spectroscopy of nuclear spin isomer separated H₂O@C and D₂O@C

Gas-phase electronic spectra of H2O@C60+ and D2O@C60+ are presented. These data were obtained by one-photon dissociation of weakly bound helium complexes synthesised in a 3 K ion trap. Measurements were recorded in the vicinity of the 2Ag,2Bg←X2Au electronic transitions of the C60+ cage. Two-colour hole burning experiments enabled nuclear spin isomer pure data to be obtained. The spectra are rich in structure with many absorptions attributed to internal excitation of the encapsulated molecule accompanying the C60+ electronic transition. The experimental data are complemented with density functional theory calculations using the B3LYP functional and 6-31++G** basis set.</p

The objectness of everyday life: disburdenment or engagement?

The article grew out of a conference paper, ‘The objectness of everyday life: engagement and disburdenment’, Material Geographies, UCL, September 2002. An expanded version of the paper was included in a special themed section of an issue of Geoforum. The paper intervenes into contemporary philosophical scholarship on the nature of use-value, usability, design and ethics. The article has been directly engaged with in an academic journal; Christensen, Carleton B. (2005) ‘The Material Basis of Everyday Rationality: transformation by design or education?’, Design Philosophy Papers No.4,)