We present an analytical model for intermolecular Coulombic electron capture (ICEC) which includes the internal nuclear dynamics of the molecules involved. In ICEC, an electron attaches to an atom or molecule by transferring excess energy to a neighbor, ionizing said neighbor. While previous theoretical investigations assumed fixed nuclei, recent studies indicate that relative motion between the two ICEC partners significantly influences the process. Here, we incorporate the internal nuclear motion of the molecules involved into an analytical equation of the ICEC cross section. We employ two approaches: 1. utilizing theoretical vibrationally resolved photoionization cross sections and 2. applying the Franck-Condon principle. Our theory yields electron spectra, ICEC cross sections for individual vibronic transitions, and temperature dependent cross sections. Nuclear dynamics lead to a distribution of the electronic cross section over several vibrational states and, in our model system H+ LiH, triggers dissociation of LiH during ICEC.
We present an analytical model for intermolecular Coulombic electron capture (ICEC) which includes the internal nuclear dynamics of the molecules involved. In ICEC, an electron attaches to an atom or molecule by transferring excess energy to a neighbor, ionizing said neighbor. While previous theoretical investigations assumed fixed nuclei, recent studies indicate that relative motion between the two ICEC partners significantly influences the process. Here, we incorporate the internal nuclear motion of the molecules involved into an analytical equation of the ICEC cross section. We employ two approaches: 1. utilizing theoretical vibrationally resolved photoionization cross sections and 2. applying the Franck-Condon principle. Our theory yields electron spectra, ICEC cross sections for individual vibronic transitions, and temperature dependent cross sections. Nuclear dynamics lead to a distribution of the electronic cross section over several vibrational states and, in our model system H+ LiH, triggers dissociation of LiH during ICEC.
Interparticle Coulombic Electron Capture (ICEC) provides an environment-assisted pathway for electron attachment that can compete with photorecombination. Here, we present the first comprehensive survey of ICEC in atom-atom and atom-molecule systems, screening 2442 combinations in search of promising candidates for future experimental investigation.
We employ the efficient asymptotic approximation to predict ICEC cross sections and electron spectra. Intramolecular nuclear motion is included, while interparticle nuclear dynamics is neglected to permit an extensive survey.
We identify several classes of atom-atom and atom-molecule systems with favourable ICEC cross sections and ICEC-to-photorecombination ratios, including halogen-halide systems and systems involving a proton and diatomic molecules such as N2, O2, CO, and NO. These findings point to atmospheric and astrochemical environments in which ICEC may be relevant.
Electronic decay processes provide a fascinating window into correlated electronic rearrangements occurring on ultrafast timescales. Following these dynamics in real time has become increasingly accessible experimentally, but extracting the underlying electronic dynamics from measured spectra requires understanding how nuclear motion shapes the observable signal. Here, we extend an analytical description of time-resolved electronic decay spectra to include dissociative nuclear dynamics and apply it to Interparticle Coulombic Decay (ICD) in the neon dimer. The resulting spectra reproduce the experimentally observed spectral shape and reveal an unexpectedly important role of interference between pathways involving different vibronic resonance states. We further establish a clear connection between the temporal build-up of the spectral structure and the nuclear wavepacket dynamics in the decaying electronic state. Most strikingly, our analytical expressions reveal that the time-dependent integrated ICD signal contains contributions proportional to both exp(−t/τ) and exp[−t/(2τ)]. Nevertheless, a conventional mono-exponential fit can describe the temporal signal remarkably well while yielding a decay lifetime that differs substantially from the underlying value. Applying the theoretically derived fitting model to experimental data for the neon dimer yields an ICD lifetime τ of 73 fs, rather than the previously extracted 150(50) fs, placing the experimental value within the range of previous theoretical predictions. Since the underlying temporal structure is common to electronic decay processes, our findings have implications for extracting lifetimes from time-resolved decay spectra well beyond ICD.
Scattering of K(np) Rydberg atoms by electron-attaching molecules can result in the formation of positive-negative ion pairs through electron transfer reactions. These reactions can involve the dissociation of a transient intermediate negative ion into a smaller negative ion and a neutral fragment, or they can result in the parent molecule forming a metastable negative ion, with the excess energy being distributed among its internal modes. For Rydberg atoms of intermediate n, it is possible for these ion pairs to orbit each other at large separation, weakly bound by their mutual electrostatic attraction, forming what are known as heavy-Rydberg states. Measurements of the binding energy and velocity distributions of the ion pairs are used to probe the dynamics of electron transfer reactions. The data are analyzed using a semiclassical Monte Carlo collision code to explore the lifetime of the intermediate, the nature of its dissociation, the distribution of the excess energy of reaction, and the branching ratio of the various reaction channels. Results obtained using a variety of attaching targets including CF3I, CCl4, SF6, CH2Br2, 1,1,1-C2Cl3F3, CCl3Br, Fe(CO)5, and CH3NO2 have demonstrated both the wide variety of different behaviors that can accompany electron capture as well as the different behaviors of the product ion-pair states themselves. Remarkably, despite previous work showing that it was possible for CH3NO2 to form long-lived valence-bound negative ions through Rydberg electron transfer, the present work showed that such collisions do not result in the formation of long-lived bound ion-pair states. Rather, the data show that collisions lead to very strong Rydberg atom scattering through formation of transient ion-pair states. These results are consistent with theoretical work that predicts significant collisional quenching of Rydberg atoms by highly polar molecules and highlight a new mechanism for Rydberg atom scattering.
Thermal collisions between potassium Rydberg atoms with intermediate values of quantum number n and target molecules that capture free low-energy electrons are investigated. The velocity, binding energy, and angular distributions of heavy-Rydberg ion-pair states formed through such collisions are measured. The experimental data are analyzed with the aid of semiclassical Monte Carlo simulations to investigate the dynamics of electron attachment to a variety of target species. Multiple reaction channels involving short- and long-lived intermediates are seen for electron capture by 1,1,1-C2Cl3F3 and CBrCl3 (where dissociation of CBrCl3 intermediates involves production of Br- and Cl- ions). Electron attachment to BrCN produces long-lived BrCN-* intermediates whose dissociation results in the creation of rotationally-hot CN- anions. Electron capture by Fe(CO)5 leads to formation of Fe(CO)5-* intermediates which can fragment producing Fe(CO)4- anions, either directly or after partial redistribution of the excess energy within the intermediate has occurred. Electron transfer in Rydberg atom collisions with C2Cl4 provide no evidence of formation of long-lived C2Cl4 ions, only Cl- ions are seen. Moreover, strong Rydberg atom scattering is observed following collisions of K(12p) Rydberg states with CH3NO2. This finding is consistent with a theory which predicts that collisions between Rydberg atoms with intermediate values of n and polar molecules can lead to strong resonant quenching of Rydberg states, i.e., n and l changing, through formation of short-lived K+...CH3NO2- ion-pair states. Finally, the improvements in sensitivity to electron capture reaction dynamics that might be achieved using different Rydberg species and a crossed molecular beam are examined. Simulations are performed to demonstrate that the use of a hyperthermal helium Rydberg atomic beam and a crossed beam of target molecules such as CCl4, BrCN and CF3I can provide new insights into dissociative electron attachment reactions. The calculations show that not only can much detailed information on translational energy release distributions and intermediate lifetimes be obtained, but also on the electron radial probability density distributions in the Rydberg atoms themselves.
Heavy-Rydberg ion-pair states, molecular quantum systems that are bound by their long-range pure Coulomb attraction, are formed through Rydberg atom collisions with molecules that attach low energy electrons. Collisions of potassium Rydberg atoms K(np) with the attaching species CCl4 and SF6 lead, respectively, to dissociative and non-dissociative electron attachment with subsequent formation of bound ion-pair states K+..Cl- and K+..SF6-.\nThe experimental apparatus used to produce and detect heavy-Rydberg ion-pair states consists of a reaction region and a separate analysis region. It separates a fraction of the product ion pairs from the parent Rydberg atoms, eliminating spurious background signals associated with blackbody-induced and electric-field ionization of Rydberg atoms. A position sensitive detector in the analysis region is employed to measure their velocity, angular, and binding energy distribution and lifetimes. Measurements of the spatial distribution of ion pairs provide information on their velocity and angular distributions, and their binding energy distribution is measured using electric field-induced dissociation. The lifetime of the ion-pair states is influenced by multiple processes including internal-to-translational energy transfer, autodetachment of the electron, and neutralization through charge transfer.\nThe experimental results are compared with the results of a Monte Carlo collision code that models both the initial Rydberg electron attachment and the subsequent evolution and molecular dynamics of the ion pairs. This model highlights the factors such as the kinematics of the Rydberg atom and the attaching particle and energy released in dissociation (in the case of dissociative attachment) that are important in governing ion pair formation. The model calculations are in good agreement with the experimental data.
The dynamics and processes involved in particle-molecule scattering, including nuclear dynamics, are described and analyzed using various quantum information quantities throughout the different stages of the scattering. The main process studied and characterized with the information quantities is the interatomic Coulombic electronic capture, an inelastic process that can lead to dissociation of the target molecule. The analysis focuses on a one-dimensional transversely confined NeHe molecule model used to simulate the scattering between an electron ${e}^{\ensuremath{-}}(\text{particle})$ and a NeHe+ ion (molecule). The time-independent Schr\"odinger equation is solved using the finite element method with a self-developed Julia package FEMTISE to compute potential energy curves and the parameters of the interactions between particles. The time-dependent Schr\"odinger equation is solved using the multiconfiguration time-dependent Hartree algorithm. The time-dependent electronic and nuclear probability densities are calculated for different electron incoming energies, evidencing elastic and inelastic processes that can be correlated to changes in von Neumann entropy, von Neumann mutual information, and Shannon mutual information. The expectation value of the position of the particles, as well as their standard deviations, are analyzed along the whole dynamics and related to the entanglement during the collision and after the process is over, thus highlighting the dynamics of entanglement generation. It is shown that the correlations generated in the collision are partially retained only when the inelastic process is active.