Laboratory Spectroscopy of PAHs

Pino, T.; Féraud, Géraldine; Bréchignac, Ph.; Bieske, Evan J.; Schmidt, Timothy W.

doi:10.1017/s1743921313015950

Cited by 3 publications

(4 citation statements)

References 42 publications

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“…Mass spectroscopic evidence recently demonstrated the existence of five-membered ring π-radicals in soot-forming regions of the flame. , Recent images of the aromatic molecules in flames have also revealed these partially saturated pentagonal edges on aromatic molecules. , Using electronic structure theory, we demonstrated that these partially saturated edges form highly localized π-radicals, ,, which were initially hypothesized by Abrahamson in 1977 . Spectroscopic measurements of these radicals have been undertaken in the astrochemistry community, with their fluorescence suggested to be involved in the unidentified emission from the Red Rectangle proto-planetary nebula . Of interest for formation mechanisms, localization of π-electrons was found to allow for multiple reactive sites on a single aromatic molecule (with the simplest being a diradical), which is a requirement for sustaining a chain reaction.…”

Section: Introductionmentioning

confidence: 79%

“…16 Spectroscopic measurements of these radicals have been undertaken in the astrochemistry community, with their fluorescence suggested to be involved in the unidentified emission from the Red Rectangle proto-planetary nebula. 25 Of interest for formation mechanisms, localization of π-electrons was found to allow for multiple reactive sites on a single aromatic molecule (with the simplest being a diradical), 26 which is a requirement for sustaining a chain reaction.…”

Section: ■ Introductionmentioning

confidence: 99%

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π-Diradical Aromatic Soot Precursors in Flames

et al. 2021

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Soot emitted from incomplete combustion of hydrocarbon fuels contributes to global warming and causes human disease. The mechanism by which soot nanoparticles form within hydrocarbon flames is still an unsolved problem in combustion science. Mechanisms proposed to date involving purely chemical growth are limited by slow reaction rates, whereas mechanisms relying on solely physical interactions between molecules are limited by weak intermolecular interactions that are unstable at flame temperatures. Here, we show evidence for a reactive π-diradical aromatic soot precursor imaged using non-contact atomic force microscopy. Localization of π-electrons on non-hexagonal rings was found to allow for Kekulé aromatic soot precursors to possess a triplet diradical ground state. Barrierless chain reactions are shown between these reactive sites, which provide thermally stable aromatic rim-linked hydrocarbons under flame conditions. Quantum molecular dynamics simulations demonstrate physical condensation of aromatics that survive for tens of picoseconds. Bound internal rotors then enable the reactive sites to find each other and become chemically cross-linked before dissociation. These species provide a rapid, thermally stable chain reaction toward soot nanoparticle formation and could provide molecular targets for limiting the emission of these toxic combustion products.

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Section: Introductionmentioning

confidence: 79%

Section: ■ Introductionmentioning

confidence: 99%

π-Diradical Aromatic Soot Precursors in Flames

et al. 2021

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“…None could be correlated with DIBs, and only upper limits of the column densities were inferred (Zack & Maier 2014). PAH cations have been previously studied in rare-gas matrices (Mattioda et al 2005); however, they remain a challenge for gas-phase laboratory observations (Pino et al 2014;Salama & Ehrenfreund 2014). Most often gas-phase electronic spectra were recorded by monitoring the photofragmentation of the molecule as a function of the wavelength, because large ionic species (>20 carbon atoms) have low quantum efficiencies for fluorescence and are not in high enough densities for direct absorption.…”

Section: Introductionmentioning

confidence: 99%

“…A number of electronic spectra were obtained using argon as a messenger, but the perturbations on the absorption bands are too large to make a reliable comparison with astronomical data (Pino et al 2014). A weakly bound helium atom has significantly less distortion on the observed features in the electronic spectrum (Bieske et al 1992;Chalyavi et al 2015;Campbell et al 2016b).…”

Section: Introductionmentioning

confidence: 99%

Gas-phase Electronic Spectra of Coronene and Corannulene Cations

Hardy

Rice

Maier

2017

ApJ

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Gas-phase electronic spectra of the coronene ( + C H 24 12 ) and corannulene ( + C H 20 10 ) cations complexed with helium have been recorded in a quadrupole ion trap at 5 K by photodissociation. The electronic spectrum of + C H 20 10 with two helium atoms was also measured to estimate the perturbation. This method is sufficient for an astronomical comparison because the shift due to the weakly bound helium is on the order of 0.2 Å.

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Electronic spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration

Daly,

Palotás,

Jacovella

et al. 2023

A&A

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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.

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Laboratory Spectroscopy of PAHs

Cited by 3 publications

References 42 publications

π-Diradical Aromatic Soot Precursors in Flames

π-Diradical Aromatic Soot Precursors in Flames

Gas-phase Electronic Spectra of Coronene and Corannulene Cations

Electronic spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration

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