Two-body Fragmentation Channels Research Articles

Pathways of two-body dissociation of BrCNq+ (q = 2, 3) induced by electron collision.

Pathways of two-body fragmentation of BrCNq+ (q = 2, 3) have been explored by combined experimental and theoretical studies. In the experiment, the BrCN molecule is ionized by 1keV electron impact and the created fragment ions are detected using an ion momentum imaging spectrometer. Six two-body fragmentation channels are identified. By measuring the momentum vectors of the fragment ions, the kinetic energy release (KER) distributions for these channels have been determined. Theoretically, the potential energy curves of BrCNq+ (q = 2, 3) as a function of Br-C and C-N internuclear distances are calculated by the complete active space self-consistent field method. By comparing the measured KER and theoretical predictions, pathways for the fragmentation channels are assigned. The relative branching ratios of the channels are also determined.

Three and four identical fermions near the unitary limit

This work analyzes the three and four equal-mass fermionic systems near and at the $s$- and $p$-wave unitary limits using hyperspherical methods. The unitary regime addressed here is where the two-body dimer energy is at zero energy. For fermionic systems near the $s$-wave unitary limit, the hyperradial potentials in the $N$-body continuum exhibit a universal long-range ${R}^{\ensuremath{-}3}$ behavior governed by the $s$-wave scattering length alone. The implications of this behavior on the low-energy phase shift are discussed. At the $p$-wave unitary limit, the four-body system is studied through a qualitative look at the structure of the hyperradial potentials at unitarity for the ${L}^{\ensuremath{\pi}}={0}^{+}$ symmetry. A quantitative analysis shows that there are tetramer states in the lowest hyperradial potentials for these systems. Correlations are made between these tetramers and the corresponding trimers in the two-body fragmentation channels. Universal properties related to the four-body recombination process $A+A+A+A\ensuremath{\leftrightarrow}{A}_{3}+A$ are discussed.

Exploring the influence of experimental parameters on the interaction of asymmetric ω/2ω fields with water isotopologues.

Water isotopologues are doubly ionized by phase-controlled asymmetric ω/2ω laser fields, and their two-body fragmentation channels leading to pairs of OH+/H+ [channel (I)] and H2 +/O+ [channel (II)] are systematically investigated. The dependence of the ionic fragments on phase distinguishes between two dissociation channels, while a quantity that is proportional to the directionality of the ejected fragments, called asymmetry parameter (β), is measured as a function of composite field's phase. The dependence of the two channels' asymmetry amplitude (β0) on the experimental parameters that characterize the composite field (wavelength, anisotropic shape, and total intensity) is found to differ significantly. The channel leading to H2 + and O+ ions' ejection shows increased asymmetry compared to the other channel and is found to be dependent on excitation of overtones and combinations of vibrational modes as well as from the field's shape and intensity. The asymmetry (β) of the channel leading to the release of a H+ and an OH+ ions is far less sensitive to the experimental parameters. Inspection of the individual OH+ peak's dependence on phase reveals information on the effect of the field's profile, which is unclear when asymmetry (β) is inspected.

Two-body dissociation of C3H4 isomers investigated by 50 keV/u Ne8+ impact

SynopsisFragmentation dynamics of two isomers of C3H4, propyne (CH3CCH) and allene (CH2CCH2), is in-vestigated by 50 keV/u Ne8+ impact. Isomerization processes are identified in two-body fragmentation channels of C3H4 2+ for both isomers. Besides, we observe two new dissociation channels of C3H4 3+ trications, H+ + C3H3 2+ and H2 + + C3H2 2+. For CH2CCH2 3+, the peak and shoulder structures in the kinetic energy release spectrum of H+ + C3H3 2+ channel are attributed to different geometries of the C3H3 2+ products by comparing with theoretical cal-culation.

Angular Distribution of Ion Products in the Double Photoionization of Propylene Oxide.

A photoelectron-photoion-photoion coincidence technique, using an ion imaging detector and tunable synchrotron radiation in the 18.0–37.0 eV photon energy range, inducing the ejection of molecular valence electrons, has been applied to study the double ionization of the propylene oxide, a simple prototype chiral molecule. The experiment performed at the Elettra Synchrotron Facility (Trieste, Italy) allowed to determine angular distributions for ions produced by the two-body dissociation reactions following the Coulomb explosion of the intermediate (C3H6O)2+ molecular dication. The analysis of the coincidence spectra recorded at different photon energies was done in order to determine the dependence of the β anisotropy parameter on the photon energy for the investigated two-body fragmentation channels. In particular, the reaction leading to + C2H3O+ appears to be characterized by an increase of β, from β ≈ 0.00 up to β = 0.59, as the photon energy increases from 29.7 to 37.0 eV, respectively. This new observation confirms that the dissociation channel producing and C2H3O+ final ions can occur with two different microscopic mechanisms as already indicated by the bimodality obtained in the kinetic energy released (KER) distributions as a function of the photon energy in a recent study. Energetic considerations suggest that experimental data are compatible with the formation of two different stable isomers of C2H3O+: acetyl and oxiranyl cations. These new experimental data are inherently relevant and are mandatory information for further experimental and theoretical investigations involving oriented chiral molecules and linearly or circularly polarized radiation. This work is in progress in our laboratory.

Two-body dissociation of C3H4 isomers investigated by 50 keV/u Ne8+ impact.

The fragmentation of two isomers of C3H4, propyne (CH3CCH) and allene (CH2CCH2), is investigated by 50 keV/u Ne8+ impact. Obvious isomer effects are observed by comparing the time-of-flight spectra generated from the two isomers. Six two-body fragmentation channels of C3H4 2+ dications are identified for each isomer. CH2 + + C2H2 + is found to be the most favored CC bond breaking channel for both isomers, indicating that CH3CCH2+ intends to rearrange to the structure containing the CH2 group before fragmentation. For CH bond breaking channels, it is found that the CH3CCH which contains a CH3 group is more efficient for H2 + and H3 + ejection. In addition, two-body dissociation channels of C3H4 3+ trications are identified. While the H+ + C3H3 2+ channel is observed in the fragmentation of both isomers, the H2 + + C3H2 2+ channel only occurs in the fragmentation of CH3CCH3+. For CH2CCH2 3+, the peak and shoulder structures in the kinetic energy release spectrum of the H+ + C3H3 2+ channel are attributed to different geometries of the C3H3 2+ product.

Investigation of the two- and three-fragment photodissociation of the tert-butyl peroxy radical at 248 nm.

The photodissociation dynamics of the tert-butyl peroxy (t-BuOO) radical are studied by fast-radical-beam coincidence translational spectroscopy. The neutral t-BuOO radical is formed by photodetachment of the corresponding t-BuOO- anion at 700 nm (1.77 eV), followed by dissociation at 248 nm (5.00 eV). Photofragment mass and translational energy distributions are obtained. The major channel is found to be three-body fragmentation to form O, CH3, and acetone (83%), with minor two-body fragmentation channels leading to the formation of O2 + tert-butyl radical (10%) and HO2 + isobutene (7%). Experimental results show that the translational energy distribution for two-body dissociation peaks is close to zero translational energy, with an isotropic angular distribution of fragments. These results indicate that two-body fragmentation proceeds via internal conversion to the ground electronic state followed by statistical dissociation. For three-body dissociation, the translational energy distribution peaks closer to the maximal allowed translational energy and shows an anisotropic distribution of the plane of the dissociating fragments, implying rapid dissociation on an excited-state surface. A small shoulder in the three-body translational energy distribution suggests that some three-fragment dissociation events proceed by a different mechanism, involving internal conversion to the ground electronic state followed by sequential dissociation.

Elucidating the two and three-body fragmentation channels on isotopically labeled nitrous oxide by a two-color asymmetric laser field

We report the interaction of isotopically labeled nitrous oxide (15N14N16O) time-of-flight mass spectroscopy. The phase dependence of two-body fragmentation channels for linear and circular polarization reveals that the nitrogen–nitrogen bond fission channel is in accordance with the ‘selective ionization of oriented molecules’ mechanism, while the nitrogen–oxygen bond rupture involves an electron recollision mechanism. For the three-body-fragmentation channel resulting in 14N3+ ions it is demonstrated that it may proceed via a concerted and/or a sequential manner. The phase dependence of the sequential channel is indicative of the following dissociation route: 15N14N16O→15N14N+16O→15N+14N+16O.

Strong-field dissociative double ionization of acetylene.

We investigate dissociative double ionization of acetylene, one of the smallest organic molecules yet with a rich electronic structure, in strong laser fields by measuring two fragment ions and two electrons in coincidence. The two-body fragmentation channels are dominated by the removal of electrons from the lower-lying molecular orbitals rather than from the highest occupied one. The electron localization-assisted enhanced ionization mechanism plays a central role for the strong-field deprotonation ionization of acetylene by releasing the second electron from the up-field potential well of the hydrogen site at the internuclear distance near twice the equilibrium value of the C-H bond.

Dissociative recombination of small carbon cluster cations

The dissociative recombination of small cluster cations with free, zero-energy electrons was studied at the ASTRID storage ring. It was found that only two-body fragmentation channels contribute: C+C{sub 2} for C{sub 3}{sup +}, C{sub 2}+C{sub 2} and C+C{sub 3} for C{sub 4}{sup +}. For C{sub 5}{sup +} and C{sub 6}{sup +} the final channels were also characterized by two-body fragmentation, but the specific channels were not identified because of limited mass resolution. It is being speculated whether cluster ions larger than C{sub 6}{sup +} may undergo recombination without dissociation. These clusters have a large heat capacity and a correspondingly lower temperature after electron capture. The decay of the intermediate neutral clusters may be influenced by infrared emission, which provides cooling and prevents dissociation.

Two-body fragmentation channels of three-body systems.

An asymptotic expansion of the wave functions for the fragmentation channels of three-body systems is developed in hyperspherical coordinates. It is shown that, to any finite power in 1/R, where ${\mathrm{mR}}^{2}$= is the trace of the inertia tensor, the expanded wave function is an analytic finite sum of Sturmian functions. The expansion is carried out explicitly through order 1/${R}^{4}$. These asymptotic states converge (as R\ensuremath{\rightarrow}\ensuremath{\infty}) to polarized orbitals for two-electron systems, and also provide improved dissociation channels for molecular ions, such as ${\mathrm{HD}}^{+}$. Asymptotic potential curves for He and ${\ensuremath{\mu}}^{\mathrm{\ensuremath{-}}}$-H systems are presented as illustrations.

Four-particle scattering with three-particle interactions

The four-particle scattering formalism proposed independently by Alessandrini, by Mitra et al., by Rosenberg, and by Takahashi and Mishima is extended to include a possible three-particle interaction. The kernel of the new equations we get contain both two- and three-body connected parts and gets four-body connected after one iteration. On the other hand, the kernel of the original equations in the absence of three-particle interactions does not have a two-body connected part. We also write scattering equations for the transition operators connecting the two-body fragmentation channels. They are generalization of the Sloan equations in the presence of three-particle interactions. We indicate how to include approximately the effect of a weak three-particle interaction in a practical four-particle scattering calculation.