Theoretical and experimental study of the A2Πu–X2Πg band system of C7−

Lakin, Nicholas M.; Tulej, Marek; Maier, John P.; Chambaud, Gilberte; Rosmus, P.

doi:10.1063/1.1321768

Cited by 20 publications

(14 citation statements)

References 32 publications

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“…− and C 9 − anions have been found to have openshell 2 Π g and 2 Π u ground states, respectively, from investigations using rare gas matrices, 18,[37][38][39] resonance enhanced multiphoton electron detachment, [40][41][42] and electronic structure calculations. [43][44][45] Anion photoelectron spectroscopy (PES) is a powerful technique for interrogating the vibronic structure of sizeselected neutral clusters via photodetachment of the corresponding anion.…”

Section: Introductionmentioning

confidence: 99%

Slow photoelectron velocity-map imaging of cold C7− and C9−

Babin

DeVine

Weichman

et al. 2018

The Journal of Chemical Physics

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High-resolution anion photoelectron spectra of cryogenically cooled C 7 − and C 9 − clusters obtained using slow photoelectron velocity-map imaging are presented, providing insight into the vibronic structure of neutral C 7 and C 9. These spectra yield accurate measurements of vibrational frequencies for the neutral clusters as well as electron affinities of 3.3517(4) and 3.6766(14) eV for C 7 and C 9 , respectively. In the C 7 − spectrum, transitions involving the previously unreported v 1 and v 2 symmetric stretching modes, as well as the v 9 , v 10 , and v 11 asymmetric bending modes, are assigned. Spin-orbit splitting is observed for several transitions in this spectrum, giving an energy difference of 28(6) cm −1 between the 2 Π 1/2g and 2 Π 3/2g spin-orbit levels of the C 7 − anion. In the spectrum of C 9 − , transitions involving the previously unreported symmetric stretch v 1 and the asymmetric bend v 11 are observed. In both spectra, several features are assigned to Franck-Condon forbidden transitions involving the doubly degenerate v 10 and v 11 modes of C 7 and the v 13 and v 14 modes of C 9. The appearance of these transitions is attributed to Herzberg-Teller coupling between the electronic states of the neutral clusters. Additional FC-forbidden transitions to states previously observed in gasphase infrared experiments are observed and attributed to vibronic coupling between the electronic states of the anion, resulting in non-totally symmetric character in the anion's full vibrational ground state. Finally, consideration of the energy dependence of detachment cross sections and Dyson orbital analyses reveal that addition of more carbon atoms to the linear chain results in photodetachment from delocalized molecular orbitals with increasing nodal structure, leading to threshold photodetachment cross sections that differ considerably from simple symmetry considerations.

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Section: Introductionmentioning

confidence: 99%

Slow photoelectron velocity-map imaging of cold C7− and C9−

Babin

DeVine

Weichman

et al. 2018

The Journal of Chemical Physics

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“…The high electron affinity and density of vibrational states of C 7 permits rapid radiative electron attachment such that anion formation has been calculated to occur every time an electron collides with C 7 (Terzieva & Herbst 2000). However, the early promise of C − 7 as a DIB carrier was quashed when high resolution observational and laboratory spectroscopy by Galazutdinov et al (1999), Sarre & Kendall (2000), Lakin et al (2000) and McCall et al (2001) identified that the match between the DIBs and the wavelengths, strengths and profiles of the C − 7 optical absorption bands was too poor to constitute an assignment.…”

Section: Previous Studiesmentioning

confidence: 99%

The CH$_\mathsf{2}$CN^- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?

Cordiner

Sarre²

2007

A&A

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The hypothesis that the cyanomethyl anion CH 2 CN − is responsible for the relatively narrow diffuse interstellar band (DIB) at 8037.8± 0.15 Å is examined with reference to new observational data. The 0 0 0 absorption band arising from the 1 B 1 −X 1 A transition from the electronic ground state to the first dipole-bound state of the anion is calculated for a rotational temperature of 2.7 K using literature spectroscopic parameters and results in a rotational contour with a peak wavelength of 8037.78 Å. By comparison with diffuse band and atomic line absorption spectra of eight heavily-reddened Galactic sightlines, CH 2 CN − is found to be a plausible carrier of the λ8037 diffuse interstellar band provided the rotational contour is Doppler-broadened with a b parameter between 16 and 33 km s The rotational level populations may be influenced by nuclear spin statistics, resulting in the appearance of additional transitions from K a = 1 of ortho CH 2 CN − near 8025 and 8050 Å that are not seen in currently available interstellar spectra. For CH 2 CN − to be the carrier of the λ8037 diffuse interstellar band, either a) there must be mechanisms that convert CH 2 CN − from the ortho to the para form, or b) the chemistry that forms CH 2 CN − must result in a population of K a levels approaching a Boltzmann distribution near 3 K.

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“…On the other hand, recent detailed analyses of DIB profiles have suggested that several of the stronger DIBs may be due to small molecules (≤ 7 heavy atoms) (Oka et al 2013;Huang & Oka 2015). While a number of such small molecules have been considered over the years, most detailed comparisons between laboratory and astronomical spectra have not yielded adequate matches (e.g., Tulej et al 1998;Motylewski et al 2000;Lakin et al 2000;McCall et al 2001;Guthe et al 2001;Salama et al 2011). Some five near-IR DIBs were recently attributed to the fullerene cation C 60 + Walker et al 2015; though see Galazutdinov et al 2017).…”

Section: Introductionmentioning

confidence: 99%

The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds

Fan

Welty

York

et al. 2017

ApJ

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Abstract:We study the behavior of eight diffuse interstellar bands (DIBs) in different interstellar environments, as characterized by the fraction of hydrogen in molecular form (f H2 ), with comparisons to the corresponding behavior of various known atomic and molecular species. The equivalent widths of the five "normal" DIBs (ll5780.5, 5797.1, 6196.0, 6283.8, and 6613.6), normalized to E B-V , show a "Lambda-shaped" behavior: they increase at low f H2 , peak at f H2 ~ 0.3, and then decrease. The similarly normalized column densities of Ca, Ca + , Ti + , and CH + also decline for f H2 > 0.3. In contrast, the normalized column densities of Na, K, CH, CN, and CO increase monotonically with f H2 , and the trends exhibited by the three C 2 DIBs (ll4726.8, 4963.9, and 4984.8) lie between those two general behaviors. These trends with f H2 are accompanied by cosmic scatter, the dispersion at any given f H2 being significantly larger than the individual errors of measurement. The Lambda-shaped trends suggest the balance between creation and destruction of the DIB carriers differs dramatically between diffuse atomic and diffuse molecular clouds; additional processes besides ionization and shielding are needed to explain those observed trends. Except for several special cases, the highest W l (5780)/W l (5797) ratios, characterizing the so-called "sigma-zeta effect", occur only at f H2 < 0.2. We propose a sequence of DIBs based on trends in their pair-wise strength ratios with increasing f H2 . In order of increasing environmental density, we find the l6283.8 and l5780.5 DIBs, the l6196.0 DIB, the l6613.6 DIB, the l5797.1 DIB, and the C 2 DIBs.

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Theoretical and experimental study of the A2Πu–X2Πg band system of C7−

Cited by 20 publications

References 32 publications

Slow photoelectron velocity-map imaging of cold C7− and C9−

Slow photoelectron velocity-map imaging of cold C7− and C9−

The CH$_\mathsf{2}$CN^- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?

The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds

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Theoretical and experimental study of the A2Πu–X2Πg band system of C7−

Cited by 20 publications

References 32 publications

Slow photoelectron velocity-map imaging of cold C7− and C9−

Slow photoelectron velocity-map imaging of cold C7− and C9−

The CH$_\mathsf{2}$CN- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?

The Behavior of Selected Diffuse Interstellar Bands with Molecular Fraction in Diffuse Atomic and Molecular Clouds

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The CH$_\mathsf{2}$CN^- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?