First Principles Quantum Dynamical Investigation Provides Evidence for the Role of Polycyclic Aromatic Hydrocarbon Radical Cations in Interstellar Physics

Reddy, V. Sivaranjana; Ghanta, Susanta; Mahapatra, S.

doi:10.1103/physrevlett.104.111102

Cited by 40 publications

(49 citation statements)

References 20 publications

(37 reference statements)

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“…The problem in theoretical calculations often emerges from the importance of many nuclear degrees of freedom and participation of many energetically close-lying electronic states in the dynamics of these large-sized molecules. In the recent past we examined the electronic transitions in the naphthalene and anthracene radical cations by theoretical methods based on a full quantum mechanical representation and reported close correspondence of the calculated spectra with those obtained from gas phase measurements as well as the observed DIBs [12][13][14][15].…”

Section: Introductionmentioning

confidence: 85%

Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

Reddy

Mahapatra

2012

Chemical Physics

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Section: Introductionmentioning

confidence: 85%

Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

Reddy

Mahapatra

2012

Chemical Physics

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“…2.1.1) or other carbonaceous particles such as PAHs (see e.g. Marciniak et al 2015;Reddy et al 2010). The 4430 Å DIB, however, seems the only one strong enough to allow the verification that the profile actually seems Lorentzian, as shown for this band by Snow et al (2002).…”

Section: Matching Band Profiles and Other Dib Properties?mentioning

confidence: 99%

Interstellar fullerene compounds and diffuse interstellar bands

Omont

2016

A&A

103

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Recently, the presence of fullerenes in the interstellar medium (ISM) has been confirmed and new findings suggest that these fullerenes may possibly form from polycyclic aromatic hydrocarbons (PAHs) in the ISM. Moreover, the first confirmed identification of two strong diffuse interstellar bands (DIBs) with the fullerene, C + 60 , connects the long standing suggestion that various fullerenes could be DIB carriers. These new discoveries justify reassessing the overall importance of interstellar fullerene compounds, including fullerenes of various sizes with endohedral or exohedral inclusions and heterofullerenes (EEHFs). The phenomenology of fullerene compounds is complex. In addition to fullerene formation in grain shattering, fullerene formation from fully dehydrogenated PAHs in diffuse interstellar clouds could perhaps transform a significant percentage of the tail of low-mass PAH distribution into fullerenes including EEHFs. But many uncertain processes make it extremely difficult to assess their expected abundance, composition and size distribution, except for the substantial abundance measured for C + 60 . EEHFs share many properties with pure fullerenes, such as C 60 , as regards stability, formation/destruction and chemical processes, as well as many basic spectral features. Because DIBs are ubiquitous in all lines of sight in the ISM, we address several questions about the interstellar importance of various EEHFs, especially as possible carriers of diffuse interstellar bands. Specifically, we discuss basic interstellar properties and the likely contributions of fullerenes of various sizes and their charged counterparts such as C + 60 , and then in turn: 1) metallofullerenes; 2) heterofullerenes; 3) fulleranes; 4) fullerene-PAH compounds; 5) H 2 @C 60 . From this reassessment of the literature and from combining it with known DIB line identifications, we conclude that the general landscape of interstellar fullerene compounds is probably much richer than heretofore realized. EEHFs, together with pure fullerenes of various sizes, have many properties necessary to be suitably carriers of DIBs: carbonaceous nature; stability and resilience in the harsh conditions of the ISM; existing with various heteroatoms and ionization states; relatively easy formation; few stable isomers; spectral lines in the right spectral range; various and complex energy internal conversion; rich Jahn-Teller fine structure. This is supported by the first identification of a DIB carrier as C + 60 . Unfortunately, the lack of any precise information about the complex optical spectra of EEHFs and most pure fullerenes other than C 60 and about their interstellar abundances still precludes definitive assessment of the importance of fullerene compounds as DIB carriers. Their compounds could significantly contribute to DIBs, but it still seems difficult that they are the only important DIB carriers. Regardless, DIBs appear as the most promising way of tracing the interstellar abundances of various fullerene compounds if the breakthr...

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“…The theoretical results on the structure and dynamics of these radical cations were compared with those recorded in the laboratory 7,26,27 and also stellar meaamount of laboratory [6][7][8][9][10][11][12][13][14][15][16][17][18][19] and stellar 14 spectroscopy data on these radical cations is the primary motivation behind this study. Apart from this, it appears interesting to understand the complex vibronic coupling in the electronic excited states [20][21][22]24,25,31 of these species.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study on Molecules of Interstellar Interest. II. Radical Cation of Compact Polycyclic Aromatic Hydrocarbons

Reddy

Mahapatra

2015

J. Phys. Chem. B

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Radical cations of polycyclic aromatic hydrocarbons have been postulated to be molecular carriers of diffuse spectroscopic features observed in the interstellar medium. Several important observations made by stellar and laboratory spectroscopists motivated us to undertake a detailed theoretical study attempting to validate the recorded data. In continuation of our work on this subject, we here focus on a detailed theoretical study of the doublet ground (X̃) and low-lying excited (Ã, B̃, and C̃) electronic states of the radical cation of phenanthrene, pyrene, and acenaphthene molecule. A multistate and multimode theoretical model in a diabatic electronic basis is developed here through extensive ab initio quantum chemistry calculations. Employing this model, first-principles nuclear dynamics calculations are carried out to unravel the spectral assignment, time-dependent dynamics, and photostability of the mentioned electronic states of the radical cations. The theoretical results compare well with the observed experimental data.

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First Principles Quantum Dynamical Investigation Provides Evidence for the Role of Polycyclic Aromatic Hydrocarbon Radical Cations in Interstellar Physics

Cited by 40 publications

References 20 publications

Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

Theoretical study of electronic absorption spectroscopy of propadienylidene molecule vis-â-vis the observed diffuse interstellar bands

Interstellar fullerene compounds and diffuse interstellar bands

Theoretical Study on Molecules of Interstellar Interest. II. Radical Cation of Compact Polycyclic Aromatic Hydrocarbons

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