Atomic and Molecular Beams, some recent Developments

Tosi, Paolo, Bassi, Davide

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.

Roger Campargue

Gerard Meijer

Abstract State-selective manipulation of beams of atoms and molecules with electric and magnetic fields has been crucial for the success of the field of molecular beams. Originally, this manipulation only involved the transverse motion. In this Chapter, the development of the Stark-decelerator, that allows to also manipulate and control the longitudinal motion of molecules in a beam, is presented.

Isidor Isaac Rabi, E. Montaldi

Timothy J. McCarthy, Michaël T. Timko, Dudley R. Herschbach

Deflection by magnetic or electric field gradients has long been used to analyze or to alter the translational trajectories of neutral gas-phase atoms or molecules. Recent work has developed sources of slow, cold molecular beams that offer means to enhance markedly the attainable deflections, which are inversely proportional to the translational kinetic energy. The sensitivity and resolution can thus be much increased, typically by factors of 10(2)-10(4). We illustrate ways to exploit this enhanced deflection capability, particularly when balancing electric and magnetic deflections. Chemical scope can be greatly extended by utilizing feeble but ubiquitous interactions, especially the induced electric dipole due to the molecular polarizability and magnetic moments resulting from molecular rotation or nuclear spins. We also examine the effect of non-Maxwellian velocity distributions produced by supersonic expansions or by quantum statistics (pertinent for ultracold beams). Generic plots are provided, employing dimensionless variables, to facilitate the design and interpretation of experiments with deflections amplified by low kinetic energy.