Atomic and molecular beam experiments

Tosi, Paolo, Bassi, Davide

Cyril Bernard Lucas

Atomic and molecular beams are employed in physics and chemistry experiments and, to a lesser extent, in the biological sciences. These beams enable atoms to be studied under collision-free conditions and allow the study of their interaction with other atoms, charged particles, radiation, and surfaces. Atomic and Molecular Beams: Production and Col

Heinrich Gerhard Kuhn

E. L. Leasure, Charles R. Mueller, Thomas Y. Ridley

A molecular beam source for high-energy metastable atoms, utilizing a corona discharge, is described. It was designed for scattering experiments where accurate alignment of beam components is required. The metastable atoms produced in this source have kinetic energies from 5 to 74 eV dependent on the species and sufficient velocity selection to reveal structure in the differential cross sections. These high-energy metastables were previously reported as photons. When the molecular beam source was operated at 200–300 Torr, a supersonic beam of metastables was produced. An optimization of operating conditions produced a supersonic beam flux two orders of magnitude greater than previously reported.

V. B. Leonas

Kevin E. Strecker, David W. Chandler

Recently we developed a technique for producing cold molecules from a supersonic molecular beam via single collisions with a supersonic atomic beam [M. S. Elioff, J. J. Valentini, and D. W. Chandler, Science 302, 1940 (2003)]. This cooling technique necessarily produces the cold molecules at the relatively high density crossing of the atomic and molecular beams. In previous reports, secondary glancing collisions with the remnant atomic and molecular beams lead to rapid depletion of the cold molecules limiting the observation time to less than $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$ with an estimated temperature of $440\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. Here we present experimental conditions for the kinematic cooling technique which overcome the limitations of the previous experiments. We demonstrate the success of this experiment for the production of cold nitric oxide (NO) in the ground vibrational, $j=7.5$ rotational, state in order to compare with our previously reported data. With the present setup, we are able to extract the cold molecules from the pulsed molecular and atomic beams and we observe these cold $\mathrm{NO}{(X)}_{j=7.5}$ persisting for over $150\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{s}$. This long observation time demonstrates our ability to temporally and spatially separate the cold molecules from the parent atomic and molecular beams, simultaneously allowing for a better measurement of the final average velocity for the kinematically cooled molecules. From the data we find a final average velocity of the $\mathrm{NO}{(X)}_{j=7.5}$ of approximately $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{m}∕\mathrm{s}$, consistent with simulations. The final observed average velocity is equated to a temperature of approximately $35\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$, over an order of magnitude colder than our previous measurements.