Ultrafast Studies on the Photophysics of Matrix-Isolated Radical Cations of Polycyclic Aromatic Hydrocarbons

Zhao, Liang; Lian, Rui; Shkrob, Ilya A.; Crowell, Robert A.; Pommeret, S.; Chronister, Eric L.; Liu, An Dong; Trifunac, A. D.

doi:10.1021/jp021832h

Cited by 38 publications

(43 citation statements)

References 35 publications

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“…It is interesting to note that more than 50% of the observed DIB features have bandwidths between 2 and 5 cm −1 , which cannot be attributed to PAH ions because of their short lifetimes ͑ϳ0.2 ps͒ and broader bandwidths ͑20-30 cm −1 ͒. 15,17,54 We conclude from this study that neutral PAHs are probably more important for these narrow DIB features.…”

Section: Discussionmentioning

confidence: 64%

Cavity ring-down spectroscopy and theoretical calculations of the S1(B3u1)←S(Ag1) transition of jet-cooled perylene

Tan

Salama

2005

The Journal of Chemical Physics

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As part of our long-term program to test the diffuse interstellar band-polycyclic aromatic hydrocarbon hypothesis, we have investigated the S(1)<--S(0) electronic transition of neutral perylene (C(20)H(12)) in a combined experimental and theoretical study. Jet-cooled perylene was prepared with a pulsed discharge slit nozzle and detected by cavity ring-down spectroscopy. A number of vibronic features were observed in the 24 000-24 900 cm(-1) spectral range. Density functional and ab initio calculations were performed to determine the geometries, harmonic vibrational frequencies, and normal coordinates of both the S(0) and S(1) electronic states. A rotational temperature of 52+/-5 K was derived from a rotational contour analysis of the vibronic band associated with the 0-0 transition. A Franck-Condon treatment was carried out to calculate the vibronic spectrum of the S(1)<--S(0) transition. A good agreement was found between the calculated and the experimental spectra. A vibrational assignment is proposed and six normal modes are identified. The contribution of neutral compact polycyclic aromatic hydrocarbons to the diffuse interstellar bands is briefly discussed.

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Section: Discussionmentioning

confidence: 64%

Cavity ring-down spectroscopy and theoretical calculations of the S1(B3u1)←S(Ag1) transition of jet-cooled perylene

Tan

Salama

2005

The Journal of Chemical Physics

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“…The latest experimental studies of cold, gas-phase PAHs and PAH cations reveal that neutral (i.e., closed shell) PAHs exhibit electronic absorption line widths that are consistent with those observed for the majority of the DIBs (ca. 3 cm À1 ; Tan & Salama 2005), while PAH radical cations exhibit line widths that are far broader (i.e., 20-30 cm À1 ) than the typical DIB (Biennier et al 2003;Sukhorukov et al 2004;Zhao et al 2004). This striking difference can be traced to differences in the intrinsic lifetimes of the excited states accessed by electronic absorptions in the closed-shell (neutral) and open-shell (radical cation) species.…”

Section: Electronic Spectroscopy Of Interstellar Panhsmentioning

confidence: 95%

Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

Hudgins

Bauschlicher

Allamandola

2005

ApJ

281

304

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This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 m interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies of the spectroscopic properties of large (>30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 m emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton). In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene + (C 24 H þ 12 ), ovalene + (C 32 H þ 14 ), circumcoronene + (C 54 H þ 18 ), and circum-circumcoronene + (C 96 H þ 24 ). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied. These alternative classes of PAH variants include (1) oxygen-and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations.Overall, the studies reported here demonstrate that increasing PAH size alone is insufficient to account for the position of the shortest wavelength interstellar 6.2 m emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or more nitrogen atoms within the interior of the carbon skeleton of a PAH cation induces a significant blueshift in the position of the dominant CC stretching feature of these compounds that is sufficient to account for the position of the interstellar bands. Subsequent studies of the effects of substitution by other heteroatoms (O and Si), metal ion complexation ( Fe + , Mg + , and Mg 2+ ), and molecular symmetry variation-all of which fail to reproduce the blueshift observed in the PANH cations-indicate that N appears to be unique in its ability to accommodate the position of the interstellar 6.2 m bands while simultaneously satisfying the other constraints of the astrophysical problem. This result implies that the peak position of the interstellar feature near 6.2 m traces the degree of nitrogen substitution in the population, that most of the PAHs responsible for the interstellar IR emission features incorporate nitrogen within their aromatic networks, and that a lower limit of 1%-2% of the cosmic nitrogen is sequestered within the interstellar PAH populati...

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“…The reason for this lies mostly in their elusive nature, having excited-state lifetimes of a few picoseconds or less. 152,[154][155][156][157][158][159][160] This property, in combination with the finite rate of their production upon CS, prevents the build-up of significant and detectable transient concentrations. However, strong evidence of the formation of excited ions has recently been obtained by measuring, using transient IR absorption spectroscopy, how the energy dissipated upon ultrafast CS and CR is redistributed into the vibrational modes of the reaction partners.…”

Section: Excited Ionsmentioning

confidence: 99%

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

Rosspeintner

Vauthey

2014

Phys. Chem. Chem. Phys.

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Because of their key role in many areas of science and technology, bimolecular photoinduced electron transfer reactions have been intensively studied over the past five decades. Despite this, several important questions, such as the absence of the Marcus inverted region or the structure of the primary reaction product, have only recently been solved while others still remain unanswered. Ultrafast spectroscopy has proven to be extremely powerful to monitor the entire electron transfer process and to access, with the help of state-of-the-art theoretical models of diffusion-assisted reactions, crucial information like e.g. the intrinsic charge separation dynamics beyond the diffusion limit. Additionally, extension of these experimental techniques to other spectral regions than the UV-visible, such as the infrared, has given a totally new insight into the nature, the structure and the dynamics of the key reaction intermediates, like exciplexes and ions pairs. In this perspective, we highlight these recent progresses and discuss several aspects that still need to be addressed before a thorough understanding of these processes can be attained.

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Ultrafast Studies on the Photophysics of Matrix-Isolated Radical Cations of Polycyclic Aromatic Hydrocarbons

Cited by 38 publications

References 35 publications

Cavity ring-down spectroscopy and theoretical calculations of the S1(B3u1)←S(Ag1) transition of jet-cooled perylene

Cavity ring-down spectroscopy and theoretical calculations of the S1(B3u1)←S(Ag1) transition of jet-cooled perylene

Variations in the Peak Position of the 6.2 μm Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

Bimolecular photoinduced electron transfer reactions in liquids under the gaze of ultrafast spectroscopy

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