Temperature behavior of infrared spectra of polycyclic aromatic hydrocarbons and the Unidentified Infrared Bands

Blanco, A.; Fonti, S.; Orofino, V.

doi:10.1086/169396

Cited by 7 publications

(4 citation statements)

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“…The effect of temperature on the IR spectra of PAHs has been studied experimentally. It was first reported in the solid phase (KBr and CsI pellets) for temperatures up to 500 K. − Most of these studies evidenced band shifts toward lower wavenumbers (toward the red) with increasing temperature. Joblin et al recorded the spectra of gas-phase pyrene (C 16 H 10 ), coronene (C 24 H 12 ), and ovalene (C 32 H 14 ) up to ∼900 K. They showed that, in the studied temperature range, the band positions and widths follow a linear trend with temperature, whose slopes are given by the coefficients χ′ and χ″ for the band positions and widths, respectively.…”

Section: Introductionmentioning

confidence: 99%

“…10 Several experimental studies have been performed to study the effect on anharmonicity on the infrared (IR) spectra of PAHs. The effect of temperature was first reported in the solid phase (KBr and CsI pellets) for temperatures up to 500 K. [11][12][13][14] Most of these studies evidenced band shifts towards lower wavenumbers (towards the red) with increasing temperature. Joblin et al 7 derived that the band positions and widths follow a near-linear dependence with temperature, based on high-temperature gas-phase data obtained for pyrene (C 16 H 10 ), coronene (C 24 H 12 ), and ovalene (C 32 H 14 ) up to ∼900 K. Empirical effective anharmonicity factors were derived to quantify these slopes for the most intense bands.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K

et al. 2019

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Quantifying the effect of anharmonicity on the infrared spectrum of large molecules such as polycyclic aromatic hydrocarbons (PAHs) at high temperature is the focus of a number of theoretical and experimental studies, many of them motivated by astrophysical applications. We recorded the infrared spectrum of pyrene C 16 H 10 microcrystals embedded in a KBr pellet over a wide range of temperature (14 -723 K) and studied the evolution of band positions, widths and integrated intensities with temperature. We identified jumps for some of the spectral characteristics of some bands in the [423-473] K range. These were attributed to a change of phase from crystal to molten in condensed pyrene, which appears to affect more strongly bands involving large CH motions. Empirical anharmonic factors that describe the evolution of band positions and widths with temperature were retrieved from both phases over an unprecedented temperature range. The derived values were found to be consistent with available gas-phase data. We provide recommended values for anharmonic factors and conclude about the interest of the methodology to provide data of interest for comparison with theoretical models and as inputs of models that simulate the infrared emission of astro-PAHs.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K

et al. 2019

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“…Several authors investigated experimentally the anharmonicity shift of small PAH molecules for temperatures up to 1000 K such as coronene, chrysene, methylcoronene, and pyrene in the solid phase ,− and naphthalene, pyrene, coronene, and ovalene in the gas phase. , These works revealed a linear profile of the band position and the bandwidth with the temperature. To quantify these trends, the slopes of these linear profiles’ χ′ and χ″ coefficients (respectively, for the band position and the bandwidth) are usually adopted.…”

Section: Discussion On Anharmonicity Effectsmentioning

confidence: 99%

Aromatic and Acetylenic C–H or C–D Stretching Bands Anharmonicity Detection of Phenylacetylene by UV Laser-Induced Vibrational Emission

et al. 2022

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The anharmonic infrared (IR) emission spectra of phenylacetylene C6H5CCH and an isotopologue C6H5CCD induced by 193 nm UV excitation have been investigated in the gas phase. The study has been operated with a homemade IR spectrometer enabling to record time- and wavelength-resolved spectra between 2.5 and 4.5 μm, emitted all along the collisional cooling. The analysis is supported by a kinetic Monte Carlo simulation in the vibrational harmonic approximation. For both species, the anharmonic shifts of the acetylenic C–H or C–D stretching modes and the aromatic C–H stretching modes are studied for band positions and bandwidths in terms of the internal energy. For C6H5CCD, the internal energy dependence of the emission intensity band ratio is investigated and rationalized. This work demonstrates the potential of time-resolved IR emission spectroscopy to explore anharmonicity of astrophysically relevant molecules.

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“…Laboratory studies have revealed many characteristic IR spectral properties of PAHs, but have mostly been limited to wavelengths below 20 µm (above 500 cm −1 ), which do not involve the truly global modes. Matrix isolation spectroscopy studies have mostly focussed on neutral PAH species, partially due to difficulties in discriminating signal originating from ions from those from absorption by neutral species (Leger et al 1989;Blanco et al 1990;Moutou et al 1995;Mattioda et al 2009;Cataldo et al 2013;Zhang & Sander 2017). Other difficulties including impurities and backgrounds exist for gasphase FT-IR or emission spectroscopy (Kurtz 1992;Zhang et al 1996;Cané et al 1997;Pirali et al 2006Pirali et al , 2009Pirali et al , 2013Goubet & Pirali 2014).…”

Section: Introductionmentioning

confidence: 99%

Gas-phase spectroscopy of photostable PAH ions from the mid- to far-infrared

Wiersma,

Candian,

Bakker

et al. 2021

Preprint

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We present gas-phase InfraRed Multiple Photon Dissociation (IRMPD) spectroscopy of cationic phenanthrene, pyrene, and perylene over the 100-1700 cm −1 (6-95 µm) spectral range. This range covers both local vibrational modes involving C-C and C-H bonds in the mid-IR, and large-amplitude skeletal modes in the far-IR. The experiments were done using the 7T Fourier-Transform Ion Cyclotron Resonance (FTICR) mass spectrometer integrated in the Free-Electron Laser for Intra-Cavity Experiments (FELICE), and findings were complemented with Density Functional Theory (DFT) calculated harmonic and anharmonic spectra, matching the experimental spectra well. The experimental configuration that enables this sensitive spectroscopy of the strongly-bound, photo-resistant Polycyclic Aromatic Hydrocarbons (PAHs) over a wide range can provide such high photon densities that even combination modes with calculated intensities as low as 0.01 km•mol −1 near 400 cm −1 (25 µm) can be detected. Experimental frequencies from this work and all currently available IRMPD spectra for PAH cations were compared to theoretical frequencies from the NASA Ames PAH IR Spectroscopic Database to verify predicted trends for far-IR vibrational modes depending on PAH shape and size, and only a relatively small redshift (6-11 cm −1 ) was found between experiment and theory. The absence of spectral congestion and the drastic reduction in bandwidth with respect to the mid-IR make the far-IR fingerprints viable candidates for theoretical benchmarking, which can aid in the search for individual large PAHs in the interstellar medium.

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Temperature behavior of infrared spectra of polycyclic aromatic hydrocarbons and the Unidentified Infrared Bands

Cited by 7 publications

References 0 publications

Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K

Experimental Approach to the Study of Anharmonicity in the Infrared Spectrum of Pyrene from 14 to 723 K

Aromatic and Acetylenic C–H or C–D Stretching Bands Anharmonicity Detection of Phenylacetylene by UV Laser-Induced Vibrational Emission

Gas-phase spectroscopy of photostable PAH ions from the mid- to far-infrared

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