Dissociation, Predissociation, and Recombination of Diatomic Molecules.

Herzberg, G.

doi:10.1086/144044

Cited by 18 publications

(5 citation statements)

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“…We have employed velocity-map imaging (VMI) and multiphoton ionization to observe the photodissociation of C2. It dissociates through predissociation of the e 3 Πg state at high vibrational levels (31), as predicted by Herzberg (20). From careful analysis of the images, we determined a BDE of 50,390.5 ± 2.4 cm −1 , bringing the precision into line with other homonuclear diatomics.…”

Section: Discussionsupporting

confidence: 70%

“…The Swan bands were first reported as the origin of the green hue of cometary comae in 1868 (19). In the 1930s, it was suggested that excitation to the newly discovered e 3 Πg state would result in photodissociation, thereby explaining why the coma of a comet was green but the tail was not (20). Empirically, astronomers place a lifetime on cometary C2 of 10 5 s at 1 AU (21,22).…”

Section: Comets | Dicarbon | Photodissociationmentioning

confidence: 99%

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Photodissociation of dicarbon: How nature breaks an unusual multiple bond

Borsovszky

Nauta

Jiang

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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The dicarbon molecule (C2) is found in flames, comets, stars, and the diffuse interstellar medium. In comets, it is responsible for the green color of the coma, but it is not found in the tail. It has long been held to photodissociate in sunlight with a lifetime precluding observation in the tail, but the mechanism was not known. Here we directly observe photodissociation of C2. From the speed of the recoiling carbon atoms, a bond dissociation energy of 602.804(29) kJ·mol−1 is determined, with an uncertainty comparable to its more experimentally accessible N2 and O2 counterparts. The value is within 0.03 kJ·mol−1 of high-level quantum theory. This work shows that, to break the quadruple bond of C2 using sunlight, the molecule must absorb two photons and undergo two “forbidden” transitions.

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Section: Discussionsupporting

confidence: 70%

Section: Comets | Dicarbon | Photodissociationmentioning

confidence: 99%

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

Borsovszky

Nauta

Jiang

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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“…In this work, the TC-RFWM method is applied to investigate the heavily perturbed v = 6 vibrational level of the d 3 g state. This vibrational level has been shown by Fox and Herzberg 25,26 to be responsible for the so-called high pressure (HP) bands. The term refers to a strikingly enhanced emis-sion from v = 6 in respect to other vibrational levels.…”

Section: Introductionmentioning

confidence: 94%

Shedding light on a dark state: The energetically lowest quintet state of C$_2$2

Bornhauser

Sych

Knopp

et al. 2011

The Journal of Chemical Physics

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In this work we present a deperturbation study of the $d\,^3\Pi _g, v=6$d3Πg,v=6 state of C$_{2}$2 by double-resonant four-wave mixing spectroscopy. Accurate line positions of perturbed transitions are unambiguously assigned by intermediate level labeling. In addition, extra lines are accessible by taking advantage of the sensitivity and high dynamic range of the technique. These weak spectral features originate from nearby-lying dark states that gain transition strength through the perturbation process. The deperturbation analysis of the complex spectral region in the (6,5) and (6,4) bands of the Swan system ($d^3\Pi _g-a\,^3\Pi _u$d3Πg−a3Πu) unveils the presence of the energetically lowest high-spin state of C$_{2}$2 in the vicinity of the $d\,^3\Pi _g, v=6$d3Πg,v=6 state. The term energy curves of the three spin components of the d state cross the five terms of the $1\;^5\Pi _g$15Πg state at rotational quantum numbers N ⩽ 11. The spectral complexity for transitions to the v = 6 level of $d\,^3\Pi _g$d3Πg state is further enhanced by an additional perturbation at N = 19 and 21 owing to the $b\, ^3\Sigma _g^-, v=19$b3Σg−,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}$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 $d\,^3\Pi _g, v=6$d3Πg,v=6 state that exhibit significant $^5\Pi _g$5Πg character through which all population flows from one electronic state to the other.

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“…The argument that follows will therefore be applicable to either configuration of activated complex if we take as our starting point the common requirement (8) In the case of an exothermic reaction the bond A-B being formed is stronger than the bond B-C being broken. The absence of any experimental evidence for these complexes (which would be metastable molecules) makes it most probable that their prediction arises from an inadequacy in the approximation.1 2 A common feature of both the linear and the triangular activated complex [Figs.…”

Section: A Exchange Reactionsmentioning

confidence: 99%

“…Equation (8) requires that AB shall be extended so that the attraction between A and B, calculated for an isolated AB molecule, equals the attraction between Band C, for isolated BC. There is, therefore, a solution to Eq.…”

Section: A Exchange Reactionsmentioning

confidence: 99%

Energy Distribution Among Reagents and Products of Atomic Reactions

Polanyi

1959

The Journal of Chemical Physics

126

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A simple valence bond resonance description of the activated complex in exothermic reactions A+BC→AB+C, coupled with experimental and theoretical evidence concerning the efficiency of transfer of vibrational energy at a collision, leads to the prediction that almost the entire heat of reaction will be contained in vibration of the bond being formed. The predicted activated complex configuration, which involves extended internuclear separation in the bond being formed, may be connected with increased collision diameters. The high efficiency of association reactions A+A+M→A2+M requires that in these reactions also the product contains almost the entire heat of reaction in vibration of the bond being formed. An attempt is made to account for the hitherto unexplained negative activation energy of these reactions in terms of the collisional redissociation of the highly vibrating product; a value for Eact of the required order of magnitude is obtained. The rate of the endothermic processes which constitute the reverse of the above reactions will be greatest if the molecule under attack is vibrationally excited. This is discussed in relation to the rate equation and is illustrated from experiment. For ``linear'' reaction the argument of the paper can be formulated in terms of potential-energy surfaces; this is done in order to illustrate points of similarity and divergence from earlier theories. Further evidence is adduced for the predicted activated complex configuration by an alternative method of calculation applied to the reaction H+Cl2→HCl+Cl. Twenty-three particular cases of exothermic exchange reactions and association reactions are discussed, in each of which some experimental evidence exists for the presence of more than equilibrium vibrational energy in the bond formed.

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Dissociation, Predissociation, and Recombination of Diatomic Molecules.

Cited by 18 publications

References 0 publications

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

Photodissociation of dicarbon: How nature breaks an unusual multiple bond

Shedding light on a dark state: The energetically lowest quintet state of C$_2$2

Energy Distribution Among Reagents and Products of Atomic Reactions

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