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LOW TEMPERATURE CHEMICAL REACTOR

Marin Pichler, W. C. Stwalley

Published Jan 1, 1998• 0 citations
OpenAlex

Abstract

A new approach for production of very cold molecules is described. This includes an experimental system for producing and observing $Cs^{\\ast}+H_{2}\\rightarrow CS$ chemical reactions below 10 K. The ground state Cs atoms are trapped and cooled down to few hundred microKelvin in a standard magneto-optical trap (MOT), and then excited to the $7 P_{1/2}$ or $7 P_{3/2}$ state. A cold para $H_{2}$ beam (up to 10 K) collides with $Cs^{+}$ atoms. Due to the reaction energetics, the CsH molecules produced by the $7 P_{1/2}$ reaction must be in the lowest rovibrational state. Detection techniques to be employed include LIF and REMPI.

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Optics Express•May 10, 2012•9 citations
A new approach for production of very cold molecules is described. This includes an experimental system for producing and observing Csast+H2rightarrowCSCs^{\\ast}+H_{2}\\rightarrow CSCsast+H2​rightarrowCS chemical reactions below 10 K. The ground state Cs atoms are trapped and cooled down to few hundred microKelvin in a standard magneto-optical trap (MOT), and then excited to the 7P1/27 P_{1/2}7P1/2​ or 7P3/27 P_{3/2}7P3/2​ state. A cold para H2H_{2}H2​ beam (up to 10 K) collides with Cs+Cs^{+}Cs+ atoms. Due to the reaction energetics, the CsH molecules produced by the 7P1/27 P_{1/2}7P1/2​ reaction must be in the lowest rovibrational state. Detection techniques to be employed include LIF and REMPI.
Several different experiments involving the making of cold and ultracold molecules are performed and proposed. Ultracold cesium molecules are produced in a magneto-optical trap (MOT) by photoassociation near the 6P j, 7Pj, 9S 1/2, 6D3/2, 7D3/2 and doubly excited asymptotes. Perturbation effects related to resonant channel coupling were observed in photoassociation spectra below the 6 P1/2 asymptote. Such effects are used to illustrate a ground state ultracold molecule formation mechanism, which can also be formed in one step photoassociation to the double minimum 31S+m state. In addition, a new technique of making cold molecules of cesium hydride is proposed, using a cold hydrogen beam source and a cesium MOT. Due to reaction energetics, the formed CsH molecules should be in their lowest rovibrational states. ^
Control over the quantum states of atoms and molecules can lead to a fundamentally new understanding of how these particles interact and react. This knowledge has the potential to impact our ability to probe processes in planetary atmospheres and in the interstellar medium. Experimental techniques developed for control and measurement of atoms are now being used to study more and more complex molecules. We study these rich systems at low temperatures, where we can trap and examine their properties for many minutes, as compared to small fractions of a second in standard experiments. Using these cold, trapped molecular ions, we investigate mechanisms of ion-molecule reactions to gain insights into the mechanisms driving these processes.
We developed a magneto-optical trap reaction microscope (MOTREMI) for strontium atoms by combining multiparticle coincident detection with the laser cooling technique. The present compact injection system enables the production of cold Sr atoms in three modes of two-dimensional (2D) magneto-optical trap (MOT) beam, molasses, and three-dimensional (3D) MOT, providing adjustable densities and ratios of the ground state 5s25{s}^{2}5s2 (1S0^{1}S_{0}1S0​) and the excited states 5s5p1P15s5p{\phantom{\rule{4pt}{0ex}}}^{1}{P}_{1}5s5p1P1​ and 3PJ^{3}P_{J}3PJ​. The target profiles including temperature, density, and size of the 3D MOT as well as the 2D MOT beam cold atomic flux were characterized in detail. Using the present setup, we investigate the single photoionization of Sr atoms with molasses through few-photons absorption in 800 nm, where Sr+{\mathrm{Sr}}^{+}Sr+ and ${e}^{\ensuremath{-}}$ are detected in coincidence and most of the ionization channels are identified. The momentum resolution for coincident Sr+{\mathrm{Sr}}^{+}Sr+ and ${e}^{\ensuremath{-}}$ along time-of-flight direction are achieved up to 0.12 a.u. and 0.02 a.u., respectively. The spectra of photoelectron ionized from the ground state as well as several excited states show distinct structures manifesting prominent contributions from multiphoton absorption. Detecting complete vector momenta of electrons and recoil ions in coincidence paves a way for further investigation of two-electron correlation dynamics and multielectron effects with alkaline-earth atoms.
A two-color magneto-optical trap (MOT) for trapping cesium (Cs) atoms is experimentally realized. This two-color MOT employs the radiation forces due to photon scattering from the Cs 6P(3/2) F' = 5 - 8S(1/2) F" = 4 excited-state transition, which replaced one pair of the three pairs of cooling/trapping laser beams operating on a single-photon red detuning to the Cs 6S(1/2) F = 4 - 6P(3/2) F' = 5 cycling transition in a standard six-beam Cs MOT, and can cool and trap atoms on both the red-detuning and blue-detuning sides of the two-photon resonance. Employing the two-color MOT, the background-free fluorescence detection of trapped atoms has been demonstrated. This technique will be useful for observation of weak fluorescence signal radiated from single atoms in MOT.