The Rb+-Rb collision rate in the energy range of 103-104 K

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 approximate to 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.