Formation and Evolution of Circumstellar and Interstellar PAHs: A Laboratory Study

Contreras, Cesar S.; Ricketts, Claire L.; Salama, Farid

doi:10.1051/eas/1146021

Cited by 8 publications

(6 citation statements)

References 11 publications

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“…2,5−11 These ubiquitous unidentified infrared bands (UIB) are thought to contain spectroscopic signatures of molecules that constitute the interstellar medium (ISM); hence identification of these suspected molecules through spectroscopic assignments could help to determine the chemical composition of the ISM. 12,13 The close match between the UIB spectra and transitions of several functional groups of aromatic molecules alludes to the possibility of PAHs in the ISM. 2,5,7,14,15 The existence of PANHs has been postulated because of their relatively strong bands between 1000 and 1750 cm −1 ; a region associated with the C−N−C in-plane vibrations.…”

Section: ■ Introductionmentioning

confidence: 98%

“…When one or more nitrogen atoms are included in the molecular frame, the resulting molecule is denoted as PANH. Spectroscopy of PAHs and PANHs is not only of interest from a fundamental point of view but also of practical value in the fields of astrophysics and astrobiology. − Infrared (IR) and far-infrared (FIR) bands have been observed to emanate from deep space since the 1970s and more recently by the Herschel space telescope and the Stratospheric Observatory for Infrared Astronomy. ,− These ubiquitous unidentified infrared bands (UIB) are thought to contain spectroscopic signatures of molecules that constitute the interstellar medium (ISM); hence identification of these suspected molecules through spectroscopic assignments could help to determine the chemical composition of the ISM. , The close match between the UIB spectra and transitions of several functional groups of aromatic molecules alludes to the possibility of PAHs in the ISM. ,,,, The existence of PANHs has been postulated because of their relatively strong bands between 1000 and 1750 cm –1 ; a region associated with the C–N–C in-plane vibrations. − The presence of stray interstellar ionizing radiations further suggests the possibility of ionized PAHs and PANHs. ,, From the perspective of astrobiology, PAHs and PANHs are of particular interest because of their potential relation to the origin of life through the formation of primitive organic molecules, including ribonucleic acids in a pre-DNA environment. , Fundamentally, comparative studies of PAHs and PANHs are also of interest in physical chemistry; nitrogen substitution into the molecular frame of a polycyclic aromatic hydrocarbon lowers the molecular symmetry and interrupts the aromaticity of the molecule. ,, …”

Section: Introductionmentioning

confidence: 99%

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Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

2015

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We report zero kinetic energy (ZEKE) photoelectron spectroscopy of benzo[h]quinoline (BhQ) via resonantly enhanced multiphoton ionization (REMPI) through the first electronically excited state S1. From the simulated REMPI spectra with and without Herzberg-Teller coupling, we conclude that vibronic coupling plays a minor but observable role in the electronic excitation to the S1 state. We further compare the S1 state of BhQ with the first two electronically excited states of phenanthrene, noticing a similarity of the S1 state of BhQ with the second electronically excited state S2 of phenanthrene. In the ZEKE spectra of BhQ, the vibrational frequencies of the cationic state D0 are consistently higher than those of the intermediate neutral state, indicating enhanced bonding upon ionization. The sparse ZEKE spectra, compared with the spectrum of phenanthrene containing rich vibronic activities, further imply that the nitrogen atom has attenuated the structural change between S1 and D0 states. We speculate that the nitrogen atom can withdraw an electron in the S1 state and donate an electron in the D0 state, thereby minimizing the structural change during ionization. The origin of the first electronically excited state is determined to be 29,410 ± 5 cm(-1), and the adiabatic ionization potential is determined to be 65,064 ± 7 cm(-1).

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Section: ■ Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

2015

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“…Due to its chemical reactivity, ethylene is one of the most important organic molecules expected to arise in a C-rich circumstellar environment (Millar et al 2000; Woods et al 2003; Cernicharo 2004; Agúndez & Cernicharo 2006). Ethylene can be involved in the growth of hydrocarbons and in the formation of PAHs or dust grains (Contreras et al 2011).…”

Section: Introductionmentioning

confidence: 99%

The Abundance of C₂H₄ in the Circumstellar Envelope of IRC+10216

Fonfría

Hinkle

Cernicharo

et al. 2017

ApJ

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High spectral resolution mid-IR observations of ethylene (C H 2 4 ) toward the AGB star IRC+10216 were obtained using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). 80 ro-vibrational lines from the 10.5μm vibrational mode n 7 with J30 were detected in absorption. The observed lines are divided into two groups with rotational temperatures of 105 and 400K (warm and hot lines). The warm lines peak at ;−14 kms −1 with respect to the systemic velocity, suggesting that they are mostly formed outwards from   R 20 . The hot lines are centered at −10kms −1 indicating that they come from a shell between 10 and  R 20 . 35% of the observed lines are unblended and can be fitted with a code developed to model the emission of a spherically symmetric circumstellar envelope. The analysis of several scenarios reveals that the C H 2 4 abundance relative to H 2 in the range 5−20R å is´-6.9 10 8 on average and it could be as high as 1.1×10 −7 . Beyond  R 20 , it is 8.2×10 −8 . The total column density is (6.5±3.0)×10 15 cm −2 . C H 2 4 is found to be rotationally under local thermodynamical equilibrium (LTE) and vibrationally out of LTE. One of the scenarios that best reproduce the observations suggests that up to 25% of the C H 2 4 molecules at  R 20 could condense onto dust grains. This possible depletion would not significantly influence the gas acceleration although it could play a role in the surface chemistry on the dust grains.

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“…[3][4][5][6][7][8] The molecular structure and chemical stability of PAH and PANH also render them potential candidates related to the origin of life in the universe. [4][5][6][9][10][11][12] While PAHs can be formed by the incomplete combustion of hydrocarbons, PANH molecules can form under similar conditions, but in a nitrogen-rich environment.…”

Section: Introductionmentioning

confidence: 99%

Electronic spectra and excited-state dynamics of acridine and its hydrated clusters

Harthcock

Zhang

Kong

et al. 2017

The Journal of Chemical Physics

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We combine results from several different experiments to investigate the photophysics of acridine (Ac) and its hydrated clusters in the gas phase. Our findings are also compared with results from condensed phase studies. Similar to measurements of Ac dissolved in hydrocarbons, the lifetime of the first electronically excited state of isolated Ac in vacuum is too short for typical resonantly enhanced multiphoton ionization (REMPI) and laser induced fluorescence (LIF) experiments, hence no signal from REMPI and LIF can be attributed to monomeric Ac. Instead, sensitized phosphorescence emission spectroscopy is more successful in revealing the electronic states of Ac. Upon clustering with water, on the other hand, the lifetimes of the excited states are substantially increased to the nanosecond scale, and with two water molecules attached to Ac, the lifetime of the hydrated cluster is essentially the same as that of Ac in aqueous solutions. Detailed REMPI and ultraviolet-ultraviolet hole-burning experiments are then performed to reveal the structural information of the hydrated clusters. Although the formation of hydrogen bonds results in energy level reversal and energy separation between the first two excited states of Ac, its effect on the internal geometry of Ac is minimal, and all clusters with 1-3 water molecules demonstrate consistent intramolecular vibrational modes. Theoretical calculations reveal just one stable structure for each cluster under supersonic molecular beam conditions. Furthermore, different from mono- and di-water clusters, tri-water clusters consist of a linear chain of three water molecules attached to Ac. Consequently, the fragmentation pattern in the REMPI spectrum of tri-water clusters seems to be dominated by water trimer elimination, since the REMPI spectrum of Ac·W is largely reproduced in the Ac mass channel, but not in the Ac·W or Ac·W channel.

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Formation and Evolution of Circumstellar and Interstellar PAHs: A Laboratory Study

Cited by 8 publications

References 11 publications

Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

The Abundance of C₂H₄ in the Circumstellar Envelope of IRC+10216

Electronic spectra and excited-state dynamics of acridine and its hydrated clusters

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Formation and Evolution of Circumstellar and Interstellar PAHs: A Laboratory Study

Cited by 8 publications

References 11 publications

Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

Zero Kinetic Energy Photoelectron Spectroscopy of Benzo[h]quinoline

The Abundance of C2H4 in the Circumstellar Envelope of IRC+10216

Electronic spectra and excited-state dynamics of acridine and its hydrated clusters

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The Abundance of C₂H₄ in the Circumstellar Envelope of IRC+10216