Experiments with an ion-neutral hybrid trap: cold charge-exchange collisions
- 651 Downloads
Due to their large trap depths (∼1 eV or 10,000 K), versatility, and ease of construction, Paul traps have important uses in high-resolution spectroscopy, plasma physics, and precision measurements of fundamental constants. An ion-neutral hybrid trap consisting of two separate but spatially concentric traps [a magneto-optic trap (MOT) for the neutral species and a mass-selective linear Paul trap for the ionic species] is an ideal apparatus for sympathetic cooling. However, over the past few years, hybrid traps have proven most useful in measuring elastic and charge-exchange rate constants of ion-neutral collisions over a wide temperature range from kilo-Kelvin to nano-Kelvin. We report some initially surprising results from a hybrid trap system in our laboratory where we have loaded the Paul trap with Ca+ ions in the presence of a Na MOT (localized dense gas of cold Na atoms). We find a strong loss of Ca+ ions with MOT exposure, attributed to an exothermic, non-resonant ion-neutral charge-exchange process with an activation barrier, which leads to the formation of Na+ ions. We propose a detailed mechanism for this process. We obtain an estimated measure of the rate constant for this charge exchange of ∼2 × 10−11 cm3/s, much less than the Langevin rate, which suggests that the Langevin assumption of unit efficiency in the reaction region is not correct in this case.
KeywordsCharge Exchange Entrance Channel Paul Trap Effective Core Potential Trapping Time
W.S. acknowledges support for the experiments from the National Science Foundation (NSF) under Grant No. PHY0855570. The work of S.B. was supported in part by the U.S. Department of Energy, Office of Basic Energy Sciences, and the work of R.C. by NSF Grant No. PHY-1101254.
- 5.W.W. Smith, E. Babenko, R. Côté, H.H. Michels, On the collisional cooling of co-trapped atomic and molecular ions by ultracold atoms: Ca+ + Na and Na2+(v*,J*) + Na. In: N.P. Bigelow, J.H. Eberly, C.R. Stroud, I.A. Walmsley (eds) Coherence and quantum optics VIII (No.8)., (Kluwer Academic/Plenum, UK, 2003) pp. 623–624.CrossRefGoogle Scholar
- 8.W.G. Rellergert, S.T. Sullivan, S. Kotochigova, A. Petrov, K. Chen, S.J. Schowalter, E.R. Hudson, Measurement of a large chemical reaction rate between ultracold closed-shell 40Ca atoms and open-shell 174Yb+ ions held in a hybrid atom-ion trap. Phys. Rev. Lett. 107(24), 243201 (2011)ADSCrossRefGoogle Scholar
- 19.F.H.J. Hall, E. Pascal, G. Hegi, M. Roault, M. Aymar, O. Dulieu, S. Willitsch, Ion-neutral chemistry at ultralow energies: dynamics of reactive collisions between laser cooled Ca+ ions and Rb atoms in an ion-atom hybrid trap. arXiv:1302.4682 [physics.atom-ph] (2013)Google Scholar
- 20.S. Haze, S. Hata, M. Fujinaga, T. Mukaiyama, Observation of elastic collisions between lithium atoms and calcium ions. arXiv, p. 1305.3346v1 (2013)Google Scholar
- 25.P.C. Stancil, S. Lepp, A. Dalgarno, The lithium chemistry of the early universe. Astrophys. J. 458, (1996)Google Scholar
- 31.S. Schwarz, Simulations for ion traps buffer gas cooling. in Trapped Charged Particles and Fundamental Interactions, volume 749 of Lecture Notes in Physics. (Springer, Berlin / Heidelberg, 2008), pp. 1–21Google Scholar
- 34.H.-J. Werner et al. version 2010.1, http://www.molpro.net
- 35.S. Banerjee et al., Chem. Phys. Lett., 542, 138 (2012)Google Scholar
- 36.S. Banerjee, Electronic structure calculations and properties of alkaline-earth molecular ions, April 2013. Ph.D. thesis, see http://digitalcommons.uconn.edu/dissertations/26/
- 37.M. Aymar, O. Dulieu, Journal of Chemical Physics, 122, 204302 (2005)Google Scholar
- 38.M. Krosnicki, E. Czuchaj, H. Stoll, Theo. Chem. Accts., 110, 28 (2003)Google Scholar