Photoassociation Spectroscopy in Penning Ionization Reactions at Sub-Kelvin Temperatures

Abstract

Penning ionization reactions in merged beams with precisely controlled collision energies have been shown to accurately probe quantum mechanical effects in reactive collisions. A complete microscopic understanding of the reaction is, however, faced with two major challenges-the highly excited character of the reaction's entrance channel and the limited precision of even the best stateof-the-art ab initio potential energy surfaces. Here, we suggest photoassociation spectroscopy as a tool to identify the character of orbiting resonances in the entrance channel and probe the ionization width as a function of inter-particle separation. We introduce the basic concept and discuss the general conditions under which this type of spectroscopy will be successful.

Quantum control of molecular rotation

“…This is somewhat unsatisfactory since even for diatomics, the best, currently available potential energy curves are not sufficiently accurate to correctly predict the scattering length and thus the exact position and partial wave character of orbiting and shape resonances [371]. An alternative would be provided by combining Penning ionization in merged beams with photoassociation spectroscopy [381] where the rotational progression of the photoassociation spectrum would allow for identifying the resonance character.…”

Single-Source, Collinear Merged-Beam Experiment for the Study of Reactive Neutral–Neutral Collisions

“…The study of atomic and molecular collisions in the few-partial wave regime offers intriguing insights into the physical nature of a collision complex. At collision energies E c / k B (where k B denotes the Boltzmann constant) below 1 K, purely quantum-mechanical phenomenasuch as barrier tunneling and quantum reflectioncan be observed since the long-range centrifugal barrier becomes very shallow and individual partial-wave contributions are no longer washed out due to thermal averaging. , The low-energy conditions also allow for the formation of exotic long-range molecules, which can potentially be studied in supersonic beam experiments using photoassociation spectroscopy. , …”

Imaging Recoil Ions from Optical Collisions between Ultracold, Metastable Neon Isotopes

“…Noble gas atoms posses a long-lived metastable state which is amenable to the methods of laser-cooling and trapping [4,5], leading to ultracold (<mK), dense (> 10 10 /cm 3 ) samples, in which collisional processes occur predominantly in the quantum regime, where only a few partial waves contribute. However, a major difficulty arises for quantum mechanical calculations of these reaction processes, owing to the coupling of the entrance molecular channel to the ionization continuum [6], and the highly excited nature of the reactants [7].…”

“…An appreciable microscopic understanding of these reactions stems from an agreement between state of the art, relativistic ab initio potentials and ionization widths, and ample, precise experimental input. Experiments investigating single or dual species ultracold collisions, usually measure trap loss and ionization rates [7][8][9][10][11][12], and in some implementations employ mass-spectroscopic techniques for separating the reaction products [13][14][15][16]. Thus, theoretical calculations, which have many degrees of freedom, are calibrated by comparing to a single, global quantity such as a reaction cross-section or the branching ratio to an ionic species [17,18].…”