Photo-associo-dissociative Ionization in a Rb MOT

M. L. Trachy, M. Shah, R. Brédy +4 more

A. Tip

Fred L. Mohler

Xiao-Kang Li, Dian-Cheng Zhang, Shuang-Fei Lv +9 more

Abstract We study both theoretically and experimentally the energy dependence of the low-energy Rb + –Rb total collision rate k ia in the energy range from 10 3 to 10 4 K. We calculate the integral elastic cross-section and the resonant charge-transfer cross-section by the quantum mechanical molecular orbital close-coupling method, and then obtain k ia for temperatures by averaging the cross-sections over a Maxwell–Boltzmann velocity distribution. The experiments are conducted in an ion–neutral hybrid trap, where the Rb + ions are created by photo-ionization of the cold atoms in a magneto-optic trap (MOT) and accumulated in the linear Paul ion trap. The total ion–atom collision rate k ia is measured by monitoring the fluorescence reduction of the steady-state MOT atoms by sequentially introducing photo-ionization and ion–atom collisions. The ion–atom collision energy E col ≈ T i is modified by changing T i due to T i being more than six orders of magnitude larger than the T a of cold atoms. The temperature of ions T i is obtained by comparing the time-of-flight mass spectrometry of Rb + from experimental results to that obtained by SIMION simulation. The equilibrium steady T i is modified by changing the initial root-mean-squared position of the ion cloud, and the k ia are measured with E col from 8000 to 16 000 K. Both the theoretical and experimental results show that k ia increases with E col . More specifically, the measured k ia increases rapidly with the enlargement of E col near 10 000 K. The theoretical calculation results show that k ia increases slowly with E col . The specific difference may be due to the influence of the ratio of excited states f e on the trend of k ia at different E col .

Nikolai B. Delone, В. П. Крайнов

Vladilen S Letokhov

Abstract In this and subsequent chapters, we consider are other laser methods for controlling atoms and molecules that, in contrast to all the methods discussed above in Chapters 2–8, are destructive. They result in the ionization of the atoms or molecules being controlled and the dissociation and fragmentation of molecules. All these methods are united by the capability of the particles to be ionized or dissociated in a photo selective manner, which makes it possible to detect and separate atoms or molecules of certain species. They are based on the fact that all the structural details of atoms and molecules manifest themselves in their spectra, for example, some details manifest in the spectra of atoms are the atomic weight (the number of nucleons), the number of protons (the nuclear charge and the type of element), the number of neutrons (the isotopic state), and even the excitation energy of the nucleus (the isomeric composition). This enables one to excite, and, in some cases, ionize atoms and molecules in a photo selective way and thus accomplish their photo selective excitation and separation. Figure 9.1 lists all types of photo selectivity. All of them have been successfully realized by the method of resonance multistep ionization of atoms that is considered in the present chapter. Our primary attention here is concentrated on the realization of laser control of the photo selectivity of ionization. A detailed description of this method can be found in the monographs by Letokhov (1987) and Hurst and Payne (1988).