Three-body Channels Research Articles

Fragmentation of CF4q+ (q=2,3) induced by 1-keV electron collisions

We report on an investigation on the fragmentation dynamics of $\mathrm{C}{{\mathrm{F}}_{4}}^{q+}$ $(q=2,3)$ induced by 1-keV electron collisions utilizing an ion momentum imaging spectrometer. From the time-of-flight correlation maps five dominating dissociation channels of $\mathrm{C}{{\mathrm{F}}_{4}}^{2+}$ as well as one three-body fragmentation channel of $\mathrm{C}{{\mathrm{F}}_{4}}^{3+}$ are identified. The kinetic energy release (KER) distributions for these channels are obtained and compared with the data available in the literature. The Dalitz-like momentum diagram and the Newton diagram are employed to analyze the breakup mechanism in the three-body fragmentation channel. We found that, for $\mathrm{C}{{\mathrm{F}}_{4}}^{2+}$ dissociation into ${\mathrm{F}}^{+}+\mathrm{C}{{\mathrm{F}}_{2}}^{+}+\mathrm{F}$, ${\mathrm{F}}^{+}+\mathrm{C}{\mathrm{F}}^{+}+2\mathrm{F}$, and ${\mathrm{F}}^{+}+{\mathrm{F}}^{+}+{\mathrm{CF}}_{2}$, the concerted breakup is the dominating process. Channel ${\mathrm{C}}^{+}+{\mathrm{F}}^{+}+3\mathrm{F}$ is dominated by the initial charge separation, i.e., $\mathrm{C}{{\mathrm{F}}_{4}}^{2+}\ensuremath{\rightarrow}{\mathrm{F}}^{+}+\mathrm{C}{\mathrm{F}}^{+}+2\mathrm{F}\ensuremath{\rightarrow}{\mathrm{C}}^{+}+{\mathrm{F}}^{+}+3\mathrm{F}$. With the help of the native frame method, we assigned one sequential pathway and two concerted pathways for channel $\mathrm{C}{{\mathrm{F}}_{4}}^{3+}\ensuremath{\rightarrow}{\mathrm{F}}^{+}+{\mathrm{F}}^{+}+\mathrm{C}{{\mathrm{F}}_{2}}^{+}$. The branching ratios of these pathways are determined. The momentum correlation of the fragments and the deduced KER distribution indicate that different excited states of $\mathrm{C}{{\mathrm{F}}_{4}}^{3+}$ with different geometries are responsible for these three pathways. The Coulomb explosion model simulation shows that most of the events in this channel are produced by $\mathrm{C}{{\mathrm{F}}_{4}}^{3+}$ ions that have deformed geometries from the neutral ${\mathrm{CF}}_{4}$ molecule.

Strong-field ionization of water. II. Electronic and nuclear dynamics en route to double ionization

We investigate the role of nuclear motion and strong-field-induced electronic couplings during the double ionization of deuterated water using momentum-resolved coincidence spectroscopy. By examining the three-body dicationic dissociation channel, D$^{+}$/D$^{+}$/O, for both few- and multi-cycle laser pulses, strong evidence for intra-pulse dynamics is observed. The extracted angle- and energy-resolved double ionization yields are compared to classical trajectory simulations of the dissociation dynamics occurring from different electronic states of the dication. In contrast with measurements of single photon double ionization, pronounced departure from the expectations for vertical ionization is observed, even for pulses as short as 10~fs in duration. We outline numerous mechanisms by which the strong laser field can modify the nuclear wavefunction en-route to final states of the dication where molecular fragmentation occurs. Specifically, we consider the possibility of a coordinate-dependence to the strong-field ionization rate, intermediate nuclear motion in monocation states prior to double ionization, and near-resonant laser-induced dipole couplings in the ion. These results highlight the fact that, for small and light molecules such as D$_2$O, a vertical-transition treatment of the ionization dynamics is not sufficient to reproduce the features seen experimentally in the strong field coincidence double-ionization data.

A novel observable for CP violation in multi-body decays and its application potential to charm and beauty meson decays

A novel observable measuring the CP asymmetry in multi-body decays of heavy mesons, which is called the forward-backward asymmetry induced CP asymmetry (FBI-CPA), ACPFB, is introduced. This observable has the dual advantages that 1) it can isolate the CP asymmetry associated with the interference of the S- and P-wave amplitude from that associated with the S- or P-wave amplitude alone; 2) it can effectively almost double the statistics comparing to the conventionally defined regional CP asymmetry. We also suggest to perform the measurements of FBI-CPA in some three-body decay channels of charm and beauty mesons.

Tracking the nuclear movement of the carbonyl sulfide cation after strong-field ionization by time-resolved Coulomb-explosion imaging

We studied the ultrafast nuclear dynamics during the dissociation of ${\mathrm{OCS}}^{+}$ molecules using a strong IR-laser pump and probe technique in combination with the coincidence measurement. The nuclear movement is tracked by analyzing the time-dependent kinetic energy release (KER) spectra. The involved dissociation states and pathways are assigned with the help of the semiclassical Landau-Zener surface hopping calculations. The real-time bond-breaking dynamics of the ${3}^{2}\phantom{\rule{0.16em}{0ex}}A{}^{\ensuremath{'}}$ coupling to other states are observed for the two-body dissociation channel and the three-body dissociation channel but with high KER. The three-body dissociation channel with low KER is assigned to the direct breaking process from the ${3}^{2}\phantom{\rule{0.16em}{0ex}}A{}^{\ensuremath{''}}$ state. The overall agreements between the experimental and theoretical results demonstrate that the time-resolved Coulomb-explosion imaging is a valuable way to monitor the bond breaking and structural evolution of complex molecules.

Dissociative ionization of OCS induced by highly charged ion impact

Dissociation of $\mathrm{OC}{\mathrm{S}}^{q+}$ $(q=3--7)$ produced by $18\text{\ensuremath{-}}\mathrm{keV}/\mathrm{u}\phantom{\rule{0.16em}{0ex}}{\mathrm{Ne}}^{8+}$ ion impact has been investigated using recoil ion momentum spectroscopy. Ten complete three-body Coulomb fragmentation channels were analyzed. Scattered projectile charge state $({\mathrm{Ne}}^{7+} \mathrm{or} {\mathrm{Ne}}^{6+})$ differentiated branching ratios and the kinetic-energy release (KER) distributions were analyzed for different fragmentation channels. Through Dalitz plots, Newton diagrams, and native frames, we have studied the concerted and sequential fragmentation mechanisms for channels leading to ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{S}}^{+}$, ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{S}}^{2+}$, ${\mathrm{O}}^{2+}+{\mathrm{C}}^{+}+{\mathrm{S}}^{+}$, and ${\mathrm{O}}^{+}+{\mathrm{C}}^{+}+{\mathrm{S}}^{3+}$. For concerted dissociation mechanisms, the molecular bending fragmentation dominates in these channels. For sequential dissociation mechanisms, the KER distribution for the dissociation of intermediate ions $\mathrm{C}{\mathrm{O}}^{2+}/\mathrm{C}{\mathrm{S}}^{2+}$ were determined and the rotation of the intermediate molecular ion $\mathrm{C}{\mathrm{O}}^{2+}$ before the second step dissociation was discussed. Thereby the relative branching ratios of events coming from sequential versus concerted mechanism were also estimated.

Energy Spectra of Alpha Particles in the Interaction of $${}^{{56}}$$Fe Nuclei with Tantalum and Uranium Nuclei at an Energy of 320 MeV

The differential cross sections for alpha-particle emission at an angle of 0 $${}^{\circ}$$ in the reactions induced by a 6-MeV/nucleon $${}^{56}$$ Fe beams incident to $${}^{238}$$ U and $${}^{181}$$ Ta targets were measured versus the alpha-particle energy by means of a high-resolution magnetic analyzer (MAVR setup). The resulting spectra were found to contain fast alpha particles of energy corresponding to the two- and three-body exit reaction channels, including alpha particles of energy close to the two-body kinematical limit. The data obtained in this experiment were analyzed on the basis of the moving-source model. The emission of nonequilibrium alpha particles in the forward direction from the heavier target nucleus upon the complete or incomplete fusion of nuclei was revealed within the time-dependent quantum approach.

Probing the top-Higgs sector with composite Higgs models at present and future hadron colliders

We study the production of toverline{t}h and toverline{t} hh at hadron colliders, in the minimal Composite Higgs Models, based on the coset SO(5)/SO(4). We explore the fermionic representations 5 and 14. A detailed phenomenological analysis is performed, covering the energy range of the LHC and its High Luminosity upgrade, as well as that of a future 100 TeV hadron collider. Both resonant and non-resonant production are considered, stressing the interplay and complementary interest of these channels with each other and double Higgs production. We provide sets of representative points with detailed experimental outcomes in terms of modification of the cross sections as well as resonance masses and branching ratios. For non-resonant production, we gauge the relative importance of Yukawa, Higgs trilinear, and contact toverline{t} hh vertices to these processes, and consider the prospect for distinguishing the fermion representations from each other and from the Standard Model. In the production of top partners, we find that the three-body decay channel W+W–t becomes significant in certain regions of parameter space having a degenerate spectrum, and is further enhanced by increasing the top partner’s mass. This motivates both higher energy machines as well as the need to go beyond the current analysis performed for the searches for these resonances.

Photoelectron photofragment coincidence spectroscopy of aromatic carboxylates: benzoate and p-coumarate.

Photoelectron-photofragment coincidence spectroscopy was used to study the dissociation dynamics of the conjugate bases of benzoic acid and p-coumaric acid. Upon photodetachment at 266 nm (4.66 eV) both aromatic carboxylates undergo decarboxylation, as well as the formation of stable carboxyl radicals. The key energetics are computed using high-level electronic structure methods. The dissociation dynamics of benzoate were dominated by a two-body DPD channel resulting in CO2 + C6H5 + e-, with a very small amount of stable C6H5CO2 showing that the radical ground state is stable and the excited states are dissociative. For p-coumarate (p-CA-) the dominant channel is photodetachment resulting in a stable radical and a photoelectron with electron kinetic energy (eKE) <2 eV. We also observed a minor two-body dissociative photodetachment (DPD) channel resulting in CO2 + HOC6H4CHCH + e-, characterized by eKE <0.8 eV. Evidence was also found for a three-body ionic photodissociation channel producing HOC6H5 + HCC- + CO2. The ion beam contained both the phenolate and carboxylate isomers of p-CA-, but DPD only occurred from the carboxylate form. For both species DPD is seen from the first and second excited states of the radical, where vibrational excitation is required for decarboxylation from the first excited radical state.

Differentiating and Quantifying Gas-Phase Conformational Isomers Using Coulomb Explosion Imaging.

Conformational isomerism plays a crucial role in defining the physical and chemical properties and biological activity of molecules ranging from simple organic compounds to complex biopolymers. However, it is often a significant challenge to differentiate and separate these isomers experimentally as they can easily interconvert due to their low rotational energy barrier. Here, we use the momentum correlation of fragment ions produced after inner-shell photoionization to distinguish conformational isomers of 1,2-dibromoethane (C2H4Br2). We demonstrate that the three-body breakup channel, C2H4+ + Br+ + Br+, contains signatures of both sequential and concerted breakup, which are decoupled to distinguish the geometries of two conformational isomers and to quantify their relative abundance. The sensitivity of our method to quantify these yields is established by measuring the relative abundance change with sample temperature, which agrees well with calculations. Our study paves the way for using Coulomb explosion imaging to track subtle molecular structural changes.

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

The kinetics of the reactions of PO with O2 and PO2 with O3 were studied at temperatures ranging from ~ 190 to 340 K, using a pulsed laser photolysis-laser induced fluorescence technique. For the reaction of PO + O2 there is evidence of both a two- and three-body exit channel, producing PO2 + O and PO3, respectively. Potential energy surfaces of both the PO + O2 and PO2 + O3 systems were calculated using electronic structure theory, and combined with RRKM calculations to explain the observed pressure and temperature dependences. For PO + O2, at pressures typical of a planetary upper atmosphere where meteoric ablation of P will occur, the reaction is effectively pressure independent with a yield of PO2 + O of > 99%; the rate coefficient can be expressed by: log10(k, 120 - 500 K, cm3 molecule-1 s-1) = -13.915 + 2.470log10(T) - 0.5020(log10(T))2, with an uncertainty of ± 10 % over the experimental temperature range (191 - 339 K). With increasing pressure, the yield of PO3 increases, reaching ~ 90% at a pressure of 1 atm and T = 300 K. For PO2 + O3, k(188 - 339 K) = 3.7 × 10-11 exp(-1131/T) cm3 molecule-1 s-1, with an uncertainty of ± 26 % over the stated temperature range. Laser induced fluorescence spectra of PO over the wavelength range of 245 - 248 nm were collected and simulated using PGOPHER to obtain new spectroscopic constants for the ground and v = 1 vibrational levels of the X2Π and A2Σ+ states of PO.

Comprehensive measurements of cross sections and spin observables of the three-body break-up channel in deuteron-deuteron scattering at 65\xa0MeV/nucleon

Detailed measurements of five-fold differential cross sections and a rich set of vector and tensor analyzing powers of the ^{2}mathrm{H}({varvec{d}},dp){n} break-up process using polarized deuteron-beam energy of 65 MeV/nucleon with a liquid-deuterium target are presented. The experiment was conducted at the AGOR facility at KVI using the BINA 4pi -detection system. We discuss the analysis procedure including a thorough study of the systematic uncertainties. The results can be used to examine upcoming state-of-the-art calculations in the four-nucleon scattering domain, and will, thereby, provide further insights into the dynamics of three- and four-nucleon forces in few-nucleon systems. The results of coplanar configurations are compared with the results of recent theoretical calculations based on the Single-Scattering Approximation (SSA). Through these comparisons, the validity of SSA approximation is investigated in the Quasi-Free (QF) region.

S wave resonance * * This work has been partially funded by COFAA-IPN (México) and by Ministerio de Ciencia e Innovación and EU FEDER (FPA2016-77177-C2-2-P, PID2019-105439GB-C22, RED2018-102572-T)

We use an existing model of the three-body system based on two-body separable interactions to study the three-body channel. For the , , and amplitudes, we have constructed separable potentials based on the most recent results of the HAL QCD Collaboration. They are characterized by the existence of a resonance just below or above the threshold in the H-dibaryon channel, . A three-body resonance appears 2.3 MeV above the threshold. We show that if the H-dibaryon channel is not considered, the S wave resonance disappears. Thus, the possible existence of a resonance would be sensitive to the interaction. The existence or nonexistence of this resonance could be evidenced by measuring, for example, the cross section.

Emission time sequence of neutrons and protons as probes of α-clustering structure * * Partially supported by the National Natural Science Foundation of China (11890714, 11421505, 11905284, 11961141003), the Strategic Priority Research Program of the CAS (XDB34030200, XDB16), and the Key Research Program of Frontier Sciences of the CAS (QYZDJ-SSW-SLH002)

Neutron–proton momentum correlation functions are constructed from a three-body photodisintegration channel, i.e., core+n+p, and used to explore the spatial-time information of the non-clustering Woods–Saxon spherical structure as well as the -clustering structures of or based on an extended quantum molecular dynamics model. The emission time sequence of neutrons and protons is indicated by the ratio of velocity-gated neutron–proton correlation functions, demonstrating its sensitivity to -clustering structures. This work sheds light on a new probe for -clustering structures.

Photodissociation dynamics of the tert-butyl perthiyl radical.

The photodissociation dynamics of the tert-butyl perthiyl (t-BuSS) radical are investigated by fast-beam coincidence translational spectroscopy. A fast (6 keV-8 keV) beam of neutral t-BuSS radicals is produced via photodetachment of the corresponding anion, followed by photodissociation at 248 nm (5.00 eV) or 193 nm (6.42 eV) and coincident detection of the neutral products. Photofragment mass and translational energy distributions are obtained at both wavelengths. At 248 nm, the dominant product channel (90%) is found to be S loss, with a product translational energy distribution that peaks close to the maximum available energy and an anisotropic photofragment angular distribution, indicating dissociation along a repulsive excited state. A minor channel (10%) leading to the formation of S2 + t-Bu is also observed. At 193 nm, both two- and three-body dissociation are observed. The formation of S2 + t-Bu is the dominant two-body product channel, with multiple electronic states of the S2 molecule produced via excited-state dissociation processes. The formation of S + t-BuS is a minor two-body channel at this dissociation energy. The three-body channels are S2 + H + isobutene, S2 + CH3 + propene, and S + SH + isobutene. The first two of these channels result from a sequential dissociation process in which the loss of S2 from t-BuSS results in ground-state t-Bu with sufficient internal energy to undergo secondary fragmentation. The third three-body channel, S + SH + isobutene, is attributed to the loss of internally excited HS2 from t-BuSS, which then rapidly dissociates to form S + SH in an asynchronous concerted dissociation process.

Dissociation of NH32+ induced by collision of 300 eV electrons with NH3

The dissociation of ammonia dications induced by 300 eV electron impact has been studied using a cold target recoil-ion momentum spectroscopy. Three regimes were found in the evolution of the produced NH32+ ions, i.e. stable (long-lived), slowly dissociating (metastable), and promptly dissociating. Multiple dissociation channels of NH32+ have been distinguished and identified by ion–ion coincidence technique. The kinetic energy release of the deprotonation dissociation channel NH32+ → H+ + NH2+ and the bond-rearrangement channel NH32+ → H2+ + NH+ have been obtained. The dynamic information and complex fragmentation pathways were analyzed by combining Dalitz plot and Newton diagram for the three-body dissociation channel NH32+ → H+ + NH+ + H. Strong correlation between the dynamic processes of H+, H loss, and the kinetic energy release was found.

Two-proton momentum correlation from photodisintegration of α -clustering light nuclei in the quasideuteron region

The proton-proton momentum correlation function is constructed in three-body photo-disintegration channels from $^{12}$C and $^{16}$O targets in the quasi-deuteron regime within the framework of an extended quantum molecular dynamics model. Using the formula of Lednicky and Lyuboshitz (LL) for the momentum correlation function, we obtain a proton-proton momentum correlation function for the specific three-body photon-disintegration channels of $^{12}$C and $^{16}$O targets, which are assumed to have different initial geometric structures, and extract their respective emission source sizes for the proton-proton pair. The results demonstrate that constructing a proton-proton momentum correlation is feasible in photo-nuclear reactions, and it is sensitive to the initial nuclear structure. For future experimental studies investigating the $\alpha$-clustering structures of light nuclei, the present work can be used to shed light on the performance and correlation function analysis of ($\gamma$,pp) or (e,$e'$pp) reactions.

Developments regarding three-body reaction channels within the R-matrix formalism

At low incident energies of nucleon-induced reaction cross sections exhibit a striking resonance structure which cannot properly be described by (semi-) microscopic models. Usually R-matrix theory is applied which provides a sufficiently accurate but phenomenological description of the resonance region. However, standard R-matrix theory is only suited for two-particle channels. Three- and many-particle channels which may occur at rather low incident energies and are usually treated in approximative or effective way. In this contribution an extension to unequal masses of the R-matrix formulation of Glockle based on the Faddeev equation is performed and proper expressions for numerical implementation are given.

Multiphoton dissociation dynamics of the indenyl radical at 248 nm and 193 nm.

Photofragment translational spectroscopy is used to investigate the unimolecular photodissociation of the indenyl radical (C9H7). C9H7 radicals are generated by photodetachment of C9H7 - anions and are dissociated at 248 nm (5.00 eV) and 193 nm (6.42 eV). The following product channels are definitively observed at both wavelengths: C2H2 + C7H5, C2H2 + C3H3 + C4H2, and C2H2 + C2H2 + C5H3. The three-body product channels are energetically inaccessible from single photon excitation at either dissociation wavelength. This observation, in combination with calculated dissociation rates and laser power studies, implies that all dissociation seen in this experiment occurs exclusively through multiphoton processes in which the initial C9H7 radical absorbs two photons sequentially prior to dissociation to two or three fragments. The corresponding translational energy distributions for each product channel peak well below the maximum available energy for two photons and exhibit similar behavior regardless of dissociation wavelength. These results suggest that all products are formed by internal conversion to the ground electronic state, followed by dissociation.

Fragmentation dynamics of nitrogen trifluoride induced by electron collision.

The fragmentation dynamics of nitrogen trifluoride (NF3) in collisions with a 500 eV electron is studied by using a momentum imaging spectrometer. The kinetic energy releases of two-body, three-body, and four-body fragmentation channels of NF3 q+ (q = 2, 3) are investigated. The fragmentation dynamics of three-body, as well as four-body, dissociation channels is analyzed by the Dalitz plot and the Newton diagram. It is found that for all of the dissociation channels, the fragment including N atom (ion) always shares significant momenta, regardless of whether it is charged. For F atom, however, it is always emitted with negligible momenta.

Photodissociation dynamics of dichlorodifluoromethane (CF2Cl2) around 235 nm using time-sliced velocity map imaging technology

Photodissociation dynamics of dichlorodifluoromethane (CF2Cl2) around 235 nm has been studied using the time-sliced velocity map imaging technology in combination with the resonance enhanced multi-photon ionization technology. By measuring the raw images of chlorine atoms which are formed via one-photon dissociation of CF2Cl2, the speed and angular distributions can be directly obtained. The speed distribution of excited-state chlorine atoms consists of high translation energy (ET) and low ET components, which are related to direct dissociation on 3Q0 state and predissociation on the ground state induced by internal conversion, respectively. The speed distribution of ground-state chlorine atoms also consists of high ET and low ET components which are related to predissociation between 3Q0 and 1Q1 states and predissociation on the ground state induced by internal conversion, respectively. Radical dissociation channel is confirmed, nevertheless, secondary dissociation and three-body dissociation channels are excluded.