Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Physical Review A

Molecular effects on antiproton capture by H2 and the states of p¯p formed

James S. Cohen

Published Nov 1, 1997• 85 citations
Publisher

Abstract

Complete five-body dynamical calculations of antiproton $(\overline{p})$ capture by the hydrogen molecule $({\mathrm{H}}_{2})$ have been carried out using a generalization of the Kirschbaum-Wilets method (belonging to a class of quasiclassical methods sometimes called fermion molecular dynamics). The differences between capture by ${\mathrm{H}}_{2}$ and the H atom are found to be dramatic. The effects due to the two-center structure, rotational motions, and vibrational motions are distinguished. Of particular importance, the vibrational degree of freedom enables the molecule to capture antiprotons having lab energies above 100 eV, whereas atomic capture cuts off sharply above the ionization threshold of 27 eV (in the lab system). Antiproton capture by the atom is calculated by the same method as well as by the classical-trajectory Monte Carlo method, which is applicable only to the atom. The initial quantum numbers (assigned quasiclassically) of the $\overline{p}p$ formed are found to be shifted to significantly smaller values for the molecular target; the $n$ distribution is also narrower for the molecular target as compared with the atomic target.

DOI
10.1103/physreva.56.3583

Related papers

Antiproton capture by simple atoms and molecules

James S. Cohen

Antiprotonic atoms form in low-energy collisions between an antiproton and a normal atom or molecule. The fermion molecular dynamics (FMD) method enables us to go beyond the atomic hydrogen target and study multielectron effects with helium and neon targets and molecular effects with hydrogen and deuterium targets. Multiple ionization and ro-vibrational excitation are found to greatly increase the maximum energy of capture, with the latter leading to a significant dependence on the projectile mass and target isotope. The kinetic energies of the ionized electrons are found to increase somewhat with the target nuclear charge.

AIP conference proceedings•Jan 1, 2000•2 citations

Exotic Rydberg atom formation in low-energy antiproton–helium collisions

Károly Tőkési, Bertalan Juhász, Joachim Burgdörfer

Exotic Rydberg atom formation in collisions between low-energy antiprotons and helium atoms is studied. We present state-selective ( n , l ) capture cross sections for antiproton-capture from 3 He and 4 He targets as a function of impact energy. The simulation is based on the 3-body classical trajectory Monte Carlo method. We find the resulting ( n , l ) distributions of captured antiprotons in good agreement with recent measurements.

Journal of Physics B Atomic Molecular and Optical Physics•Jan 6, 2005•19 citations

Exotic molecules consisting of an antiproton and a hydrogen atom

Kazuhiro Sakimoto

A theoretical study is conducted on the stability of exotic antiproton-hydrogen molecular anions ($\overline{p}\mathrm{H}$), which in the separated atom limit correlate with $\overline{p}+\mathrm{H}(n=2)$ ($n$ being the principal quantum number). The $\overline{p}\mathrm{H}$ molecule in the electronic ground state is highly unstable due to pair annihilation and autodetachment ($\ensuremath{\rightarrow}\overline{p}p+e$). However, if the $\overline{p}\mathrm{H}$ molecule is electronically excited, the molecular stability can be drastically improved. Since the excited states of the $\mathrm{H}$ atom have accidental degeneracy, the asymptotic form of the Born-Oppenheimer potential curve of $\overline{p}+\mathrm{H}(n=2)$ behaves as $1/{R}^{2}$ ($R$ being the relative distance), which can play a critical role in the bonding and stability of the molecule. It is found that the $\overline{p}\mathrm{H}$ molecule in the first electronic excited state and in a high rotational state is sufficiently stable and has a lifetime dominated by spontaneous radiative emission ($\ensuremath{\rightarrow}\overline{p}+\mathrm{H}+h\ensuremath{\nu}$). The $\overline{p}\mathrm{H}$ system is dynamically similar to ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$, which had been commonly considered to be unstable due to autodetachment. However, recent measurements of ion-beam sputtering unambiguously verified the existence of long-lived ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$ molecules in high rotational states. This suggests that the $\overline{p}\mathrm{H}$ molecules may actually be created if one employs experimental means such as the chemical sputtering of hydrogen-rich targets with $\overline{p}$ beams.

Physical Review A•Oct 8, 2018•3 citations

Formation of antiprotonic helium p¯He+ and ionization in low-energy collisions of p¯ with He in the ground 1S1 and metastable 2S3 and 2S1 states

Kazuhiro Sakimoto

Calculations of low-energy collisions of antiprotons $\overline{p}$ with helium atoms in the ground $(1\phantom{\rule{4pt}{0ex}}^{1}\mathit{S})$ and metastable $(2\phantom{\rule{4pt}{0ex}}^{3}\mathit{S}$ and $2\phantom{\rule{4pt}{0ex}}^{1}\mathit{S})$ states are carried out by using a semiclassical method and by further assuming that one of the two electrons is passive. Antiproton capture to form antiprotonic helium $(\ensuremath{\rightarrow}\overline{p}{\mathrm{He}}^{+}+e)$ and breakup ionization $(\ensuremath{\rightarrow}\overline{p}+{\mathrm{He}}^{+}+e)$ are investigated. The energy dependence of the capture and ionization cross sections and the distributions of the product states are presented and compared with previous theoretical calculations. For the metastable helium targets, most of the $\overline{p}{\mathrm{He}}^{+}$ atoms produced in the capture have long lifetimes against subsequent Auger decays and can be observed experimentally. For the ground-state targets, however, the formation of such long-lived states is rather a rare event at low collision energies.

Physical Review A•Apr 9, 2015•9 citations

Capture of negative exotic particles by atoms, ions and molecules

James S. Cohen

This article describes the capture of heavy negative particles (μ−, π−, K−, ) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, time-dependent semiclassical and quantum mechanical and quasi-classical treatments. A few of these methods, as well as the Fermi–Teller model, have also been applied to heavier atomic targets. Most of the methods, other than the quasi-classical formulations, are not yet up to treating the dynamical electron correlation and multiple ionization found to be important in capture by multi-electron atoms, or the vibronic coupling found to be important in capture by simple molecules. The essential elements of potentially more rigorous quantum mechanical theories are characterized. The experimental data on capture states and relative capture probabilities in mixtures are also discussed. The connection of this experimental data to the theoretical capture calculations is fairly tenuous, but forthcoming experiments with antiprotons promise direct tests of some of the recent theoretical findings.

Reports on Progress in Physics•Aug 21, 2004•87 citations

Long-lived states of antiprotonic lithium p¯ Li + produced in p¯+ Li collisions

Kazuhiro Sakimoto

Antiproton capture by lithium atoms ($\overline{p}+\mathrm{Li}\ensuremath{\rightarrow}\overline{p}{\mathrm{Li}}^{+}+e$) is investigated at collision energies from $0.01$ to 10 eV by using a semiclassical (also know as quantum-classical hybrid) method, in which the radial distance between the antiproton and the Li${}^{+}$ ion is treated as a classical variable, and the other degrees of freedom are described by quantum mechanics. Analyzing the wave packet of the emitted electrons and making use of the energy conservation rule enable us to calculate the state distribution of the produced antiprotonic lithium $\overline{p}{\mathrm{Li}}^{+}$ atoms and also to distinguish between the capture and ionization ($\ensuremath{\rightarrow}\overline{p}+{\mathrm{Li}}^{+}+e$) channels at collisional energies above the ionization threshold. This method is tested for the capture of negative muons by hydrogen atoms, which was rigorously investigated in previous quantum mechanical studies. Most of the $\overline{p}{\mathrm{Li}}^{+}$ atoms produced in $\overline{p}+\mathrm{Li}$ are found to be sufficiently stable against Auger decays and are experimentally observable as long-lived states. The present system bears close similarities to the system of $\overline{p}+\mathrm{He}(2S)$. It is therefore expected that long-lived antiprotonic helium $\overline{p}{\mathrm{He}}^{+}$ atoms can be efficiently produced in the $\overline{p}$ capture by metastable He($2\phantom{\rule{0.16em}{0ex}}{}^{3}S$) atoms.

Physical Review A•Sep 2, 2011•6 citations
Complete five-body dynamical calculations of antiproton (p‾)(\overline{p})(p​) capture by the hydrogen molecule (H2)({\mathrm{H}}_{2})(H2​) have been carried out using a generalization of the Kirschbaum-Wilets method (belonging to a class of quasiclassical methods sometimes called fermion molecular dynamics). The differences between capture by H2{\mathrm{H}}_{2}H2​ and the H atom are found to be dramatic. The effects due to the two-center structure, rotational motions, and vibrational motions are distinguished. Of particular importance, the vibrational degree of freedom enables the molecule to capture antiprotons having lab energies above 100 eV, whereas atomic capture cuts off sharply above the ionization threshold of 27 eV (in the lab system). Antiproton capture by the atom is calculated by the same method as well as by the classical-trajectory Monte Carlo method, which is applicable only to the atom. The initial quantum numbers (assigned quasiclassically) of the p‾p\overline{p}pp​p formed are found to be shifted to significantly smaller values for the molecular target; the nnn distribution is also narrower for the molecular target as compared with the atomic target.
Antiprotonic atoms form in low-energy collisions between an antiproton and a normal atom or molecule. The fermion molecular dynamics (FMD) method enables us to go beyond the atomic hydrogen target and study multielectron effects with helium and neon targets and molecular effects with hydrogen and deuterium targets. Multiple ionization and ro-vibrational excitation are found to greatly increase the maximum energy of capture, with the latter leading to a significant dependence on the projectile mass and target isotope. The kinetic energies of the ionized electrons are found to increase somewhat with the target nuclear charge.
A theoretical study is conducted on the stability of exotic antiproton-hydrogen molecular anions (p‾H\overline{p}\mathrm{H}p​H), which in the separated atom limit correlate with p‾+H(n=2)\overline{p}+\mathrm{H}(n=2)p​+H(n=2) (nnn being the principal quantum number). The p‾H\overline{p}\mathrm{H}p​H molecule in the electronic ground state is highly unstable due to pair annihilation and autodetachment ($\ensuremath{\rightarrow}\overline{p}p+e$). However, if the p‾H\overline{p}\mathrm{H}p​H molecule is electronically excited, the molecular stability can be drastically improved. Since the excited states of the H\mathrm{H}H atom have accidental degeneracy, the asymptotic form of the Born-Oppenheimer potential curve of p‾+H(n=2)\overline{p}+\mathrm{H}(n=2)p​+H(n=2) behaves as 1/R21/{R}^{2}1/R2 (RRR being the relative distance), which can play a critical role in the bonding and stability of the molecule. It is found that the p‾H\overline{p}\mathrm{H}p​H molecule in the first electronic excited state and in a high rotational state is sufficiently stable and has a lifetime dominated by spontaneous radiative emission ($\ensuremath{\rightarrow}\overline{p}+\mathrm{H}+h\ensuremath{\nu}$). The p‾H\overline{p}\mathrm{H}p​H system is dynamically similar to ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$, which had been commonly considered to be unstable due to autodetachment. However, recent measurements of ion-beam sputtering unambiguously verified the existence of long-lived ${\mathrm{H}}_{2}{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{-}}$ molecules in high rotational states. This suggests that the p‾H\overline{p}\mathrm{H}p​H molecules may actually be created if one employs experimental means such as the chemical sputtering of hydrogen-rich targets with p‾\overline{p}p​ beams.
Calculations of low-energy collisions of antiprotons p‾\overline{p}p​ with helium atoms in the ground (11S)(1\phantom{\rule{4pt}{0ex}}^{1}\mathit{S})(11S) and metastable (23S(2\phantom{\rule{4pt}{0ex}}^{3}\mathit{S}(23S and 21S)2\phantom{\rule{4pt}{0ex}}^{1}\mathit{S})21S) states are carried out by using a semiclassical method and by further assuming that one of the two electrons is passive. Antiproton capture to form antiprotonic helium $(\ensuremath{\rightarrow}\overline{p}{\mathrm{He}}^{+}+e)$ and breakup ionization $(\ensuremath{\rightarrow}\overline{p}+{\mathrm{He}}^{+}+e)$ are investigated. The energy dependence of the capture and ionization cross sections and the distributions of the product states are presented and compared with previous theoretical calculations. For the metastable helium targets, most of the p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ atoms produced in the capture have long lifetimes against subsequent Auger decays and can be observed experimentally. For the ground-state targets, however, the formation of such long-lived states is rather a rare event at low collision energies.
This article describes the capture of heavy negative particles (μ−, π−, K−, ) by normal atoms, ions and molecules to form exotic systems. Capture by even the hydrogen atom presents great challenges for theoretical treatment. The wide variety of methods used are reviewed, including perturbative, two-state adiabatic and diabatic, time-independent quantum mechanical, time-dependent semiclassical and quantum mechanical and quasi-classical treatments. A few of these methods, as well as the Fermi–Teller model, have also been applied to heavier atomic targets. Most of the methods, other than the quasi-classical formulations, are not yet up to treating the dynamical electron correlation and multiple ionization found to be important in capture by multi-electron atoms, or the vibronic coupling found to be important in capture by simple molecules. The essential elements of potentially more rigorous quantum mechanical theories are characterized. The experimental data on capture states and relative capture probabilities in mixtures are also discussed. The connection of this experimental data to the theoretical capture calculations is fairly tenuous, but forthcoming experiments with antiprotons promise direct tests of some of the recent theoretical findings.
Antiproton capture by lithium atoms ($\overline{p}+\mathrm{Li}\ensuremath{\rightarrow}\overline{p}{\mathrm{Li}}^{+}+e$) is investigated at collision energies from 0.010.010.01 to 10 eV by using a semiclassical (also know as quantum-classical hybrid) method, in which the radial distance between the antiproton and the Li+{}^{+}+ ion is treated as a classical variable, and the other degrees of freedom are described by quantum mechanics. Analyzing the wave packet of the emitted electrons and making use of the energy conservation rule enable us to calculate the state distribution of the produced antiprotonic lithium p‾Li+\overline{p}{\mathrm{Li}}^{+}p​Li+ atoms and also to distinguish between the capture and ionization ($\ensuremath{\rightarrow}\overline{p}+{\mathrm{Li}}^{+}+e$) channels at collisional energies above the ionization threshold. This method is tested for the capture of negative muons by hydrogen atoms, which was rigorously investigated in previous quantum mechanical studies. Most of the p‾Li+\overline{p}{\mathrm{Li}}^{+}p​Li+ atoms produced in p‾+Li\overline{p}+\mathrm{Li}p​+Li are found to be sufficiently stable against Auger decays and are experimentally observable as long-lived states. The present system bears close similarities to the system of p‾+He(2S)\overline{p}+\mathrm{He}(2S)p​+He(2S). It is therefore expected that long-lived antiprotonic helium p‾He+\overline{p}{\mathrm{He}}^{+}p​He+ atoms can be efficiently produced in the p‾\overline{p}p​ capture by metastable He(23S2\phantom{\rule{0.16em}{0ex}}{}^{3}S23S) atoms.