Dissociations of the ethyne dication C2H2+2

Thissen, R.; Delwiche, J.; Robbe, J. M.; Duflot, Denis; Flament, Jean‐Pierre; Eland, J. H. D.

doi:10.1063/1.465851

Cited by 106 publications

(137 citation statements)

References 39 publications

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“…In a previous work [31] we studied the double photoionization of acetylene molecules by using VUV synchrotron radiation at 39 eV photon energy range producing the C2H2 2+ dication dissociating by Coulomb explosion via three different two-body fragmentation channels producing the following ion pairs: H + +C2H + , CH + +CH + , and C + +CH2 + , whose threshold energies (33.8, 34.0, and 34.0 eV, respectively) were in agreement with previous experimental determinations by Eland and coworkers [37]. In the present work we have focused our attention on the characterization of the C2H2 2+ microscopic dynamical evolution towards the two-body fragmentation channels by the determination of the angular distribution of product ions, and KER, as a function of the photon energy.…”

Section: Resultssupporting

confidence: 76%

“…KER and angular distributions were obtained for all dissociation products. The results indicate a threshold for double ionization of acetylene just below 31.9 eV, in good agreement with the previous determnation of 31.7 eV [37]. Above this photon energy value, reactions (1) and (3) occur with a mechanism that appears to involve a few elementary steps through a limited number of electronic states of the intermediate C2H2 2+ dication.…”

Section: Discussionsupporting

confidence: 79%

“…In the case of reaction (3), the total kinetic energy distribution does not change significantly with the photon energy, conversely the reaction (1) exhibits a tail at higher energy, that can be fitted with two Gaussian curves. This is an indication that reaction (1) can occur with two different mechanisms [37,39]: a "slow" dissociation component in which the C2H2 2+ ion is mainly formed in its ground electronic state, with a lifetime of about 180 ns, and a "fast" dissociation component, above 37 eV, through the formation of a short lived dication in an excited electronic state, with a lifetime shorter than 50 ns. The same effect can be seen in the kinetic energy distribution of reaction (2), the symmetric one, but with a more spectacular pattern, where three components change with the photon energy, suggesting a much more complicated pattern involving several electronic states.…”

Section: Resultsmentioning

confidence: 99%

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Molecular Fragmentation of Acetylene by VUV Double Photoionization

Falcinelli

Lorent

Pirani

et al. 2017

Proceedings of the 2nd International Electronic Conference on Atmospheric Sciences

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Acetylene is a simple molecule of interest for interstellar medium (ISM) and planetary atmospheres. The presence of C2H2 was detected by IR spectroscopic measurements. Acetylene was also found as a minor component in the atmosphere of gas giants like the planet Jupiter, in the atmosphere of Saturn's satellite Titan, and in comets, where photochemical experiments have demonstrated that this simple hydrocarbon is a likely precursor of C2, a widely observed component in such environments. It has to be noted that the presence in planetary atmospheres and ISM of Vacuum Ultra Violet (VUV) light's photons as well as cosmic rays makes highly probable the double photoionization of molecular species with the production of molecular dications producing subsequent dissociation into ionic fragments having a high kinetic energy content of several eV. This translational energy is sufficient in some cases to allow ions escape from the upper atmosphere of some planet of the Solar System, as Venus, Mars and Titan, into space. In this contribution we present the experimental study of the microscopic dynamics of the two-body dissociation reactions of the C2H2 +2 dication, induced by the double ionization of acetylene molecules by VUV photons in the energy range of 31.9-50.0 eV. The photoionizing agent was a tunable synchrotron radiation beam, while ion products are revealed by coupling photoelectron-photoion-photoion-coincidence and ion imaging techniques. The measured angular distributions and kinetic energy of product ions exhibit significant changes (as the photon energy increases) for the three leading dissociation reactions producing H + +C2H + , C + +CH2 + , and CH + + CH + , providing detailed information on the fragmentation dynamics of the C2H2 2+ dication.

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Section: Resultssupporting

confidence: 76%

Section: Discussionsupporting

confidence: 79%

Section: Resultsmentioning

confidence: 99%

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Molecular Fragmentation of Acetylene by VUV Double Photoionization

Falcinelli

Lorent

Pirani

et al. 2017

Proceedings of the 2nd International Electronic Conference on Atmospheric Sciences

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“…Here, the sequential pathway is approximated as a ''stepwise'' absorption through the intermediate ionic states of ½HCCH þ . The number of photons triggering the reaction in the actual experiment can be identified by inspecting the branching ratios among the three dissociation channels, which are very sensitive to the excess energy of the photoelectrons [23,24]. The here-observed ratios of 71% for…”

Section: -2mentioning

confidence: 99%

Ultrafast Extreme Ultraviolet Induced Isomerization of Acetylene Cations

et al. 2010

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Ultrafast isomerization of acetylene cations (½HC ¼ CH þ ) in the low-lying excited A 2 AE g þ state, populated by the absorption of extreme ultraviolet (XUV) photons (38 eV), has been observed at the Free Electron Laser in Hamburg, (FLASH). Recording coincident fragments C þ þ CH 2 þ as a function of time between XUV-pump and -probe pulses, generated by a split-mirror device, we find an isomerization time of 52 AE 15 fs in a kinetic energy release (KER) window of 5:8 < KER < 8 eV, providing clear evidence for the existence of a fast, nonradiative decay channel.

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“…This prototypical dissociation pathway is interesting as it presents one of the fastest expected proton motions and can proceed via two different pathways. Figure 1A depicts the relevant cuts through the potential energy surface (PES) of acetylene along one C-H direction, including states which are relevant for the desired dissociation channel of C 2 H 2 2+ (30,31) at the present experimental conditions using a 65 fs (6.3-cycle), 3100 nm pulse (32, 33) with a peak intensity of (65 ± 16) TW/cm 2 . The pulse parameters were chosen to position the experiment in the sequential double ionization (SDI) regime in which the LIED imaging electron is ejected independently from the first electron in a second tunnel ionization step before scattering off the acetylene dication (see Supplementary Materials).…”

mentioning

confidence: 99%

Ultrafast electron diffraction imaging of bond breaking in di-ionized acetylene

Wolter

Pullen

et al. 2016

Science

288

236

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Visualizing chemical reactions as they occur requires atomic spatial and femtosecond temporal resolution. Here, we report imaging of the molecular structure of acetylene 9 fs after ionization. Using mid-infrared laser induced electron diffraction (LIED) we obtain snapshots as a proton departs the [C 2 H 2 ] 2+ ion. By introducing an additional laser field, we also demonstrate control over the ultrafast dissociation process and resolve different bond dynamics for molecules oriented parallel vs. perpendicular to the LIED field. These measurements are in excellent agreement with a quantum chemical description of fielddressed molecular dynamics. One Sentence Summary:We demonstrate space and time imaging of a single acetylene molecule after 9 fs while one of its bonds is broken and a proton departs the molecule.Ultrafast imaging of atomic motion in real time during transitions in molecular structure is prerequisite to disentangling the complex interplay between reactants and products (1, 2) since the motion of all atoms are coupled. Ultrafast absorption and emission spectroscopic techniques have uncovered numerous insights in chemical reaction dynamics (3,4), but are limited by their reliance on local chromophores and their associated ladders of quantum states rather than global structural characterization. Reaction imaging at the molecular level requires a combination of few-femtosecond temporal and picometer spatial measurement resolution (5). Amongst the many techniques that are currently under intense development, x-ray scattering can reach few-femtosecond pulse durations at photon energies of 8.3 keV (1.5 Å) (6) with a demonstrated measurement resolution of 3.5 Å (7). Challenges for such photonbased approaches are the coarse spatial resolution and the low scattering cross-sections, especially for gas phase investigations. Electron scattering (8) provides much larger interaction cross-sections and smaller de Broglie wavelengths, but suffers from space charge broadening which decreases the temporal resolution.Consequently, measurements have demonstrated 7 pm spatial and 100 fs temporal resolution (9, 10) in gas phase experiments. Remedies to improve temporal resolution include relativistic electron acceleration (11) or electron bunch compression (12) with 100 fs and 28 fs limits, respectively. Compared to such incoherent scattering of electrons from an electron source off a molecular target, laser induced electron diffraction (LIED) is a self-imaging method based on coherent electron scattering (13)(14)(15)(16)(17). In LIED, one electron which is liberated from the target molecule through tunnel ionization, it is then accelerated in the field and rescattered of its molecular ion thereby acquiring structural information. The electron recollision process occurs within one optical cycle of the laser field and permits mapping electron momenta to recollision time (18,19).Here, we used LIED to image an entire hydrocarbon molecule (acetylene -C 2 H 2 ) at 9 fs after ionizationtriggered dissociation and visualiz...

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Dissociations of the ethyne dication C2H2+2

Cited by 106 publications

References 39 publications

Molecular Fragmentation of Acetylene by VUV Double Photoionization

Molecular Fragmentation of Acetylene by VUV Double Photoionization

Ultrafast Extreme Ultraviolet Induced Isomerization of Acetylene Cations

Ultrafast electron diffraction imaging of bond breaking in di-ionized acetylene

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