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The dicarbon bonding puzzle viewed with photoelectron imaging. Nat Commun 2019; 10:5199. [PMID: 31729361 PMCID: PMC6858380 DOI: 10.1038/s41467-019-13039-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2019] [Accepted: 10/17/2019] [Indexed: 11/09/2022] Open
Abstract
Bonding in the ground state of C\documentclass[12pt]{minimal}
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\begin{document}$${}_{2}$$\end{document}2 is still a matter of controversy, as reasonable arguments may be made for a dicarbon bond order of \documentclass[12pt]{minimal}
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\begin{document}$$2$$\end{document}2, \documentclass[12pt]{minimal}
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\begin{document}$$3$$\end{document}3, or \documentclass[12pt]{minimal}
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\begin{document}$$4$$\end{document}4. Here we report on photoelectron spectra of the C\documentclass[12pt]{minimal}
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\begin{document}$${}_{2}^{-}$$\end{document}2− anion, measured at a range of wavelengths using a high-resolution photoelectron imaging spectrometer, which reveal both the ground \documentclass[12pt]{minimal}
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\begin{document}$${X}^{1}{\Sigma}_{\mathrm{g}}^{+}$$\end{document}X1Σg+ and first-excited \documentclass[12pt]{minimal}
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\begin{document}$${a}^{3}{\Pi}_{{\mathrm{u}}}$$\end{document}a3Πu electronic states. These measurements yield electron angular anisotropies that identify the character of two orbitals: the diffuse detachment orbital of the anion and the highest occupied molecular orbital of the neutral. This work indicates that electron detachment occurs from predominantly \documentclass[12pt]{minimal}
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\begin{document}$$s$$\end{document}s-like (\documentclass[12pt]{minimal}
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\begin{document}$$3{\sigma}_{\mathrm{g}}$$\end{document}3σg) and \documentclass[12pt]{minimal}
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\begin{document}$$p$$\end{document}p-like (\documentclass[12pt]{minimal}
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\begin{document}$$1{\pi }_{{\mathrm{u}}}$$\end{document}1πu) orbitals, respectively, which is inconsistent with the predictions required for the high bond-order models of strongly \documentclass[12pt]{minimal}
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\begin{document}$$sp$$\end{document}sp-mixed orbitals. This result suggests that the dominant contribution to the dicarbon bonding involves a double-bonded configuration, with 2\documentclass[12pt]{minimal}
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\begin{document}$$\pi$$\end{document}π bonds and no accompanying \documentclass[12pt]{minimal}
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\begin{document}$$\sigma$$\end{document}σ bond. In spite of its apparent simplicity, the dicarbon molecule has a bonding structure which is matter of debate. Here the authors measure high-resolution spectra of the \documentclass[12pt]{minimal}
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\begin{document}$${{\mathrm{C}}}_{2}$$\end{document}C2 anion by photoelectron imaging, revealing a bonding configuration dominated by a double \documentclass[12pt]{minimal}
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\begin{document}$$\pi$$\end{document}π bond, with no accompanying \documentclass[12pt]{minimal}
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\begin{document}$$\sigma$$\end{document}σ bond.
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Bornhauser P, Visser B, Beck M, Knopp G, van Bokhoven JA, Marquardt R, Radi PP. Experimental and theoretical investigation of the vibrational band structure of the 1 Πu5−1 Πg5 high-spin system of C2. J Chem Phys 2017; 146:114309. [DOI: 10.1063/1.4978334] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Affiliation(s)
- P. Bornhauser
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - B. Visser
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - M. Beck
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - G. Knopp
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
| | - J. A. van Bokhoven
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
- Institute for Chemical and Bioengineering, ETHZ, Zürich, Switzerland
| | - R. Marquardt
- Laboratoire de Chimie Quantique, Institut de Chimie, Université de Strasbourg 4, Rue Blaise Pascal, CS90032 67081 Strasbourg Cedex, France
| | - P. P. Radi
- Paul Scherrer Institute, CH-5232 Villigen, Switzerland
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Abstract
The unstable molecule C₂ has been of interest since its identification as the source of the "Swan band" features observable in the spectra offlames, carbon arcs, white dwarf stars, and comets, and it continues to serve as a focal point for experimental and theoretical discovery. Recent spectroscopic work has identified a quintet state of the molecule for the first time, while new insights into the bond order of C₂ in its ground state have been provided by sophisticated computational methods based on valence bond theory. This article gives a review of spectroscopic and computational work on C₂ including both historical background and the most recent discoveries.
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Bornhauser P, Sych Y, Knopp G, Gerber T, Radi PP. Shedding light on a dark state: the energetically lowest quintet state of C2. J Chem Phys 2011; 134:044302. [PMID: 21280720 DOI: 10.1063/1.3526747] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this work we present a deperturbation study of the d (3)Π(g), v=6 state of C(2) by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system (d(3)Π(g)-a (3)Π(u)) unveils the presence of the energetically lowest high-spin state of C(2) in the vicinity of the d (3)Π(g), v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the 1 (5)Π(g) state at rotational quantum numbers N ≤ 11. The spectral complexity for transitions to the v = 6 level of d (3)Π(g) state is further enhanced by an additional perturbation at N = 19 and 21 owing to the b (3)Σ(g)(-), v=19 state. The spectroscopic characterization of both dark states is accessible by the measurement of 122 "window" levels. A global fit of the positions to a conventional Hamiltonian for a linear diatomic molecule yields accurate molecular constants for the quintet and triplet perturber states for the first time. In addition, parameters for the spin-orbit and L-uncoupling interaction between the electronic levels are determined. The detailed deperturbation study unravels major issues of the so-called high-pressure bands of C(2). The anomalous nonthermal emission initially observed by Fowler in 1910 [Mon. Not. R. Astron. Soc. 70, 484 (1910)] and later observed in numerous experimental environments are rationalized by taking into account "gateway" states, i.e., rotational levels of the d (3)Π(g), v=6 state that exhibit significant (5)Π(g) character through which all population flows from one electronic state to the other.
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Affiliation(s)
- P Bornhauser
- Paul Scherrer Institute, General Energy Department, CH-5232 Villigen, Switzerland
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Mazzotti FJ, Achkasova E, Chauhan R, Tulej M, Radi PP, Maier JP. Electronic spectra of radicals in a supersonic slit-jet discharge by degenerate and two-color four-wave mixing. Phys Chem Chem Phys 2008; 10:136-41. [DOI: 10.1039/b712737e] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Burns IS, Hult J, Kaminski CF. Use of (130)Te(2) for frequency referencing and active stabilisation of a violet extended cavity diode laser. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2006; 63:905-9. [PMID: 16503188 DOI: 10.1016/j.saa.2005.10.053] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2005] [Revised: 10/28/2005] [Accepted: 10/31/2005] [Indexed: 05/06/2023]
Abstract
This paper reports on the use of (130)Te(2) absorption lines in active laser-locking, and in frequency referencing, of the emission of a violet extended cavity diode laser with a wavelength of around 410 nm. We note the existence of closely spaced tellurium absorption lines, suitable for referencing purposes in gas sensing applications, at wavelengths below the lower limit (417 nm) of the spectral region covered by the tellurium atlas [J. Cariou, P. Luc, Atlas du spectre d'Absorption de la Molecule de Tellure, CNRS, Paris, 1980]. The absolute positions of the lines in the acquired spectra were estimated by comparison to a simultaneously acquired fluorescence spectrum of atomic indium, and were identified using calculations based on fundamental spectroscopic data. The laser frequency was stabilised within a range of 40 MHz, which is negligible compared to typical transition widths at atmospheric pressure.
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Affiliation(s)
- I S Burns
- Department of Chemical Engineering, University of Cambridge, Pembroke Street, Cambridge CB2 3RA, UK.
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Abstract
The ability to separate and sort peaks is explored using a new coherent two-dimensional form of resonance Raman spectroscopy. This experimental technique distributes normally congested rotational-vibrational peaks along a series of curved lines according to vibrational sequence, rotational quantum number, and selection rule. Each line consists of rotational-vibrational peaks that have the same vibrational sequence and the same value for DeltaJ, distributed in order by rotational quantum number. For diatomic molecules, these lines originate from points where they initially travel in opposite or orthogonal directions in two-dimensional space, which helps facilitate the separation between lines. Simulations and experimental results on C2 in a flame confirm the ability to separate and sort these normally congested rotational-vibrational peaks. This method appears to provide a solution to the long-standing problems of spectral congestion and disorder in gas-phase electronic spectra.
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Affiliation(s)
- Peter C Chen
- Chemistry Department, Spelman College, 350 Spelman Lane, Atlanta, Georgia 30314, USA.
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Reichardt TA, Lucht RP. Resonant degenerate four-wave mixing spectroscopy of transitions with degenerate energy levels: Saturation and polarization effects. J Chem Phys 1999. [DOI: 10.1063/1.480354] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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Reichardt TA, Giancola WC, Shappert CM, Lucht RP. Experimental investigation of saturated degenerate four-wave mixing for quantitative concentration measurements. APPLIED OPTICS 1999; 38:6951-6961. [PMID: 18324238 DOI: 10.1364/ao.38.006951] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Degenerate four-wave mixing (DFWM) line shapes and signal intensities are measured experimentally in well-characterized hydrogen-air flames operated over a wide range of equivalence ratios. We use both low (perturbative) and high (saturating) beam intensities in the phase-conjugate geometry. Resonances in the A 2Sigma+ -X 2II (0,0) band of OH are probed with multiaxial-mode laser radiation. The effects of saturation on the line-center signal intensity and the resonance linewidth are investigated. The DFWM signal intensities are used to measure OH number densities in a series of near-adiabatic flames at equivalence ratios ranging from 0.5 to 1.5. Use of saturating pump intensities minimizes the effects of beam absorption, providing more-accurate number density measurements. The saturated DFWM results are in excellent agreement with OH absorption measurements and equilibrium calculations of OH number density. The polarization dependence of the P(1)(2) and R(2)(1) resonances is investigated in both laser intensity regimes. There is a significant change in relative reflectivities for different polarization configurations when saturated.
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Affiliation(s)
- T A Reichardt
- Department of Mechanical and Industrial Engineering, University of Illinois, 1206 West Green Street, Urbana, Illinois 61801, USA
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Zheltikov AM, Koroteev NI. Coherent four-wave mixing in excited and ionized gas media: four-photon spectrochronography, ellipsometry, and nonlinear-optical imaging of atoms and ions. ACTA ACUST UNITED AC 1999. [DOI: 10.3367/ufnr.0169.199904b.0385] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022]
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Lloyd GM, Ewart P. High resolution spectroscopy and spectral simulation of C2 using degenerate four-wave mixing. J Chem Phys 1999. [DOI: 10.1063/1.478070] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Observation of saturation dip in degenerate four-wave mixing and two-color resonant four-wave mixing spectra of jet-cooled CH. Chem Phys Lett 1998. [DOI: 10.1016/s0009-2614(98)01141-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Li H, Kong W. Polarization and probe delay effect on degenerate four wave mixing of pyrazine. J Chem Phys 1997. [DOI: 10.1063/1.474735] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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