Sympathetic crystallization of CaH+ produced by a laser-induced reaction

We investigated sympathetic Coulomb crystallization of CaH+ ions produced by a laser-induced reaction through an excited state according to Ca-40(+)(4p(2)P(1/2)) + H-2 -> (CaH+)-Ca-40 + (H center dot CaH+)-Ca-40 ions stored in a linear Paul trap were characterized by their secular-motion excitation spectrum and by the modified fluorescence images of crystallized Ca+ ions. The number of two-species crystallized ions, the secular motion temperature, and the structure were determined by molecular dynamics simulations. Both the observed two-species ion crystals and simulation images demonstrate that the CaH+ ions were sympathetically crystallized with their secular-motion temperature being less than 10 mK. We determined reaction rates from fluorescence images of two-species Coulomb crystals by systematically changing the reaction time. In addition a lower limit for the reaction rate coefficient k = 8 x 10(-10) cm(3)/s was obtained.