We report the cooling of nitric oxide molecules in a single collision between an argon atom and an NO molecule at collision energies of 5.65 {+-} 0.36 kJ/mol and 14.7 {+-} 0.9 kJ/mol in a crossed molecular beam apparatus. We have produced in significant numbers ({approx}10{sup 8} molecules cm{sup -3} per quantum state) translationally cold NO({sup 2}{Pi}{sub 1/2}, {nu}' = 0, j' = 7.5) molecules in a specific quantum state with an upper-limit laboratory-frame rms velocity of 14.8 {+-} 1.1 m/s, corresponding to a temperature of 406 {+-} 28 mK. The translational cooling results from the kinematic collapse of the velocity distribution of the NO molecules after collision. Increasing the collision energy by increasing the velocity of the argon atoms, as we do here, does shift the scattering angle at which the cold molecules appear, but does not result in an experimentally measurable change in the velocity spread of the cold NO. This is entirely consistent with our analysis of the kinematics of the scattering which predicts that the velocity spread will actually decrease with increasing argon atom velocity.
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
440mK. 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
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
NO(X)j=7.5 of approximately
4.5m∕s, consistent with simulations. The final observed average velocity is equated to a temperature of approximately
35mK, over an order of magnitude colder than our previous measurements.
We report the preparation and observation of translationally cold atoms using kinematic cooling. In these experiments, krypton atoms are cooled to subkelvin temperatures by elastic collisions in crossed atomic beams. Two independent velocity measurements indicate an upper-bound mean velocity of 13 m/s (
Etrans/k=850mK) and are consistent with a much lower mean velocity of 4 m/s (
Etrans/k=80mK) (
k is Boltzmann's constant). The density of the cold atoms is measured to be
109 atoms/cm
3. Scattering calculations and diffusion models support these velocity and density measurements. The results demonstrate that cold, dense samples of ground-state atoms and molecules can be prepared by elastic collisions between identical collision partners.
The pioneering works have demonstrated that the method of single collisions in crossed molecular beams is an important technique for achieving kinetic cool-ing of atoms or molecules in specific rotational states. In this study, we investigated the elastic and inelastic collisions between Al(2P1/2) metal atoms and O2 molecules at high collision energies in the range of 6.4–14.8 kcal/mol, utilizing the laser-ablation crossed beams in conjunction with time-sliced ion velocity map imaging tech-nique. We observed kinetic cooling of Al(2P1/2) atoms with an upper-limit laboratory-frame root-mean-square velocity of 24±3 m/s, corresponding to a translational temperature of 0.9±0.2 K in the laboratory frame, facilitated by the vibrational excitation of O2 (v′ = 1) in inelastic collisions. The translational cooling of Al atoms in the lab frame enhanced detection probability in the transformation of density-to-flux, as evidenced by the scattering images obtained during the experiments.
We have produced translationally cold ammonia (ND3) molecules in various quantum states by kinematic cooling. In these experiments, ND3 molecules are brought nearly to rest in the (J, K) = (2,0), (2,1), (2,2), (3,1), (3,2), and (3,3) rotational levels of the ground vibronic state by rotationally-inelastic collisions with Ne atoms. The cold molecules are produced in quantum-state-dependent velocity distributions whose laboratory frame velocities are measured to be between 21 m s(-1) (E(trans)/k = 530 mk) and 32 m s(-1) (E(trans)/k = 1.2 K), and are calculated to be between 7.5 m s(-1) (E(trans)/k = 70 mK) and 27 m s(-1) (E(trans)/k = 880 mK). Due to systematic experimental effects, the measured velocities are upper limits to the actual velocities. These temperatures are low enough that it should be possible to use electrostatic traps to confine cold molecules in many of these quantum states.
One possible technique is the use of a modified straight Stark guide to filter the slow moving molecules from a thermal source. Here I present such a technique and the design of the necessary apparatus. Furthermore, I present experimental results for creating a molecular source of nitric oxide (NO) whose temperature is controlled. Results showing the effects of the guide on the lowest ro-vibrational states of NO and a new technique for measuring the speed distribution of a cold molecular sample are also discussed. Finally, the use of the guide to produce cold NO molecules at a temperature of 7 +/- 2 K is described.