Two-electron capture with emission of one photon in fast collisions between a highly charged ion and a light atom

Abstract

We consider the electron capture process in fast non-relativistic ion-atom collisions in which the transfer of two electrons from the atom to the ion is accompanied by emission of one photon with the mean energy ω (2) k about two times larger than that ω(1) k characteristic for the radiative capture of one electron. Such a photon can appear both due to the uncorrelated capture process, in which two electrons are transferred to the ion independently via the Coulomb and radiative capture channels, and due to the correlated two-electron capture, where the electron-electron interaction plays the crucial role. The uncorrelated capture produces the photon spectrum which has a maximum at ω (1) k and gives the main contribution to the two-electron capture. The correlated capture mechanism leads to very small capture cross sections but produces the photon spectrum having a maximum at ∼ ω (2) k which in principle enables to separate this process in experiment.

Observation of radiative double electron capture for

“…RDEC can be used to cleanly study electron correlation if the electrons are captured to a bare projectile ion, since the two captured ions are not influenced by the neighboring electrons. RDEC has been studied experimentally [9][10][11][12][13] and theoretically [14][15][16][17][18][19][20] for more than two decades, and the first successful measurement [11] was reported in 2010 for 2.38 MeV/u O 8+ ions colliding with a thin foil carbon target. Both the REC and RDEC processes are illustrated in Figure 1.…”

Radiative double-electron capture by bare nucleus with emission of one photon

“…RDEC is a one-step process where the momentum and the energy of two correlated captured electrons are converted into energy and momentum of one emitted photon. The processes of double electron capture were investigated experimentally in [3][4][5][6] and theoretically in [7][8][9][10].…”

“…The RDEC process was investigated theoretically in [7][8][9][10]. In these works the calculations were performed within the nonrelativistic theory.…”

Triple-coalescence singularity in a dynamical atomic process

“…For that we consider the double electron capture followed by the emission of a single photon in the high energy limit. Since the first attempts to detect this process in collisions of a light atom with a heavy nucleus [5] a number of experimental [6,7] and theoretical [8,9,10] papers were devoted to this reaction.Neglecting the internal motion of the electrons in the light atom we consider the capture of two continuum electrons with equal linear momenta p 1 = 1 …”

“…At larger values of photon energies there are some additional terms corresponding to the two-step mechanism [13] in which the process can be viewed as the eN scattering followed by quasifree emission of the photon. The effects of internal motion of the target electrons [10] (in experiments the light atom is the target) provide the contributions of the order mαZ 1 /p being thus beyond the high energy limit. These effects can be incorporated into Eq.…”