Optical Absorptions of Oxygenated Carbon Chain Cations in the Gas Phase

Abstract

The gas-phase electronic spectra of linear OC4O+ and a planar C6H2O+ isomer were obtained at a rotational temperature of ≈10 K. Absorption measurements in a 6 K neon matrix were followed by gas-phase observations in a cryogenic radiofrequency ion trap. The origin bands of the transition of OC4O+ and the A B1 of HCCC(CO)CCH+ lie at 417.31 ± 0.01 nm and 523.49 ± 0.01 nm, respectively. These constitute the first electronic spectra of oxygenated carbon chain cations studied under conditions that are relevant to the diffuse interstellar bands (DIBs), as both have a visible transition. The recent analysis of the 579.5 nm DIB indicates that small carriers, five to seven heavy atoms, continue to be possible candidates (Huang & Oka 2015). Astronomical implications are discussed regarding this kind of oxygenated molecules.

Fullerenes in Space

“…Prior to this publication experiments using neon matrices showed that this is the best medium, in the absence of gas phase data, to obtain vibrationally resolved electronic spectra of open-shell cations. This strategy has ultimately allowed the electronic spectra of linear carbon chains,t heir anions and derivatives including hydrogen, nitrogen [9] and recently oxygen, [19] to be measured in the gas phase.S uch species are of relevance not only to interstellar space,b ut also in combustion and as reactive intermediates in organic chemistry. [9] From the 1990 period onward our strategy to detect the electronic transitions of larger organic cations,a nions and neutral radicals was to locate and identify these first via absorption spectra in 5K neon matrices and with this information in hand carry out the measurements in the gas phase using anumber of sensitive laser-based techniques.By 1989 we had developed an approach that enables deposition of mass-selected species,c ations or anions,t hat significantly improved the versatility of the neon matrix isolation experiment.…”

“…The corresponding neutral molecules can be subsequently generated from the mass‐selected ions in situ. This strategy has ultimately allowed the electronic spectra of linear carbon chains, their anions and derivatives including hydrogen, nitrogen and recently oxygen, to be measured in the gas phase. Such species are of relevance not only to interstellar space, but also in combustion and as reactive intermediates in organic chemistry.…”

Fullerene im Weltraum

“…Die entsprechenden neutralen Moleküle lassen sich in situ aus den masseselektierten Ionen gewinnen. Dadurch konnten wir Elektronenspektren von linearen Kohlenstoffketten, ihren Anionen und verschiedenen Derivaten einschließlich Wasserstoff‐, Stickstoff‐ und jüngst auch Sauerstoff‐Derivaten in der Gasphase messen. Solche Spezies sind nicht nur für den interstellaren Raum bedeutend, sondern auch für Verbrennungsprozesse und als reaktive Zwischenstufen in der organischen Chemie.…”

On the possible contribution of cationic oxygenated carbon chains CnO+, HCnO+, and OCnO+ (n = 4–9) to the diffuse interstellar bands

“…The composition and diversity of gaseous oxygenated carbon molecules are less understood (Herbst & Van Dishoeck 2009). Oxygen bearing carbon-rich molecules, such as oxygen-terminated carbon chains (Hardy et al 2016), are thus promising candidates for gaseous molecules participating to the oxygen budget. In the context of the DIBs, the cationic oxygenated carbon chains are of particular interest.…”

“…These absorptions are outside the spectral region of currently known DIBs. The first gas phase electronic spectra of oxygenated carbocation chains were recorded in a subsequent study by Hardy et al (2016). Spectra of linear OC 4 O + and a planar HCCC(CO)CCH + isomer were obtained by monitoring CO loss upon resonant laser excitation in a cryogenic 22-pole RF ion trap.…”