Use of heavy-Rydberg ion-pair states to probe dissociative electron attachment

Abstract

Abstract. Electron transfer in collisions between Rydberg atoms and targets that attach free low-energy electrons can lead to the formation of heavy-Rydberg ion-pair states comprising a positive-negative ion pair that orbit each other at large separations weakly bound by their mutual electrostatic attraction. It is shown that measurements of the velocity distribution of the ion-pair states produced in such collisions provide a novel probe of the dynamics of dissociative electron attachment.

Probing dissociative electron attachment through heavy-Rydberg ion-pair production in Rydberg atom collisions

“…[3][4][5][6][7] Rydberg atom collisions have been used to produce a wide variety of ion pair states for the study of their physical and chemical properties. [8][9][10][11][12][13][14] We demonstrate here that the production of ion-pair states through dissociative electron transfer reactions of the type, K(12p) + ABC → K + + ABC − * → K + ..A − + BC (4) → K + ..BC − + A, (5) where K + ..A − and K + ..BC − denote ion pair states, can also be used to elucidate the dynamics of dissociative electron capture itself. The experimental data are analyzed with the aid of a Monte Carlo collision code that models the detailed kinematics of electron transfer reactions.…”

Dissociative electron attachment studies with hyperthermal Rydberg atoms

“…The velocity and angular distributions of the product ionpair states that result from Rydberg collisions are simulated using a semi-classical Monte Carlo collision code that models the detailed kinematics of electron transfer reactions. [2][3][4][5][6]15 The model is based on the independent particle picture, and attachment is viewed as resulting from a binary interaction between the Rydberg electron and target particle. The initial velocities of the Rydberg atom and target particle are selected at random from the appropriate distribution of these quantities.…”

“…In earlier experimental studies of the velocity and angular distributions of ion-pair states produced in Rydberg atom collisions, only those ion pairs that travel within a few degrees of a fixed (horizontal) plane, i.e., atom pairs that have only a small component of transverse (vertical) velocity, were measured. [2][3][4][5][6] Such "two-dimensional" velocity distributions reflect more directly the reaction dynamics and are more straight forward to interpret. Such ion pairs are therefore identified in the simulations and it is their velocity and angular distributions that are built up by considering the outcome of many collision events.…”

“…Since many of the properties of such ion-pair states parallel those of Rydberg atoms, they are also frequently termed heavy-Rydberg states. 1 Such states have been generated not only through Rydberg atom collisions [2][3][4][5][6] but also by direct photoexcitation of ground-state diatomic molecules. 1,[7][8][9][10] Earlier Rydberg atom studies undertaken using a target gas cell and K(np) Rydberg atoms with low-to-intermediate values of n, 10 n 15, excited in a tightly collimated thermal potassium atom beam have shown that measurements of the velocity and angular distributions of the product ion-pair states can provide a window into the properties of the excited intermediates formed upon initial electron capture, including their lifetimes and the energetics of their decay.…”

Very strong Rydberg atom scattering in K(12p)–CH3NO2 collisions: Role of transient ion pair formation

“…where AB − * denotes a short-lived excited state populated by initial electron capture, AB a long-lived metastable negative ion typically formed by intramolecular vibrational relaxation, and X + • • • AB a weakly bound ion-pair state. [1][2][3][4][5][6][7][8] Since many properties of such states parallel those of Rydberg atoms, they are also frequently referred to as heavy-Rydberg states. [9][10][11][12][13] Ion-pair states represent a novel class of weakly bound, longrange molecules which, as shown by recent measurements, possess unusual physical and chemical properties.…”