The diatomic dication CuZn2+ in the gas phase.

In the present combined experimental and theoretical study we report the observation of the novel gas-phase dication CuZn(2+) and provide some theoretical insight into the electronic binding of this exotic metastable molecule and its formation mechanism. Using mass spectrometry we have detected four isotopomer signals of CuZn(2+) at half-integer m/z values for ion flight times of about 14 μs. CuZn(2+) was unambiguously identified by its isotopic abundance. High-current energetic Ar(+) ion bombardment of a brass surface was used for its production. Subsequent dication formation was found to take place in the ion extraction region of our mass spectrometer several tens of microns in front of the sputtered brass surface. The dication formation mechanism appears to be resonant electron transfer in soft gas-phase collisions between sputter-ejected singly charged CuZn(+) molecular ions and incoming Ar(+) projectiles. This conclusion is supported by our theoretical study that obtained an ionization energy of CuZn(+) of 15.75 eV, in excellent agreement with both the experimental and calculated ionization energy of Ar (15.76 and 15.67 eV, respectively). The ground state of CuZn(2+) is found to be a metastable one with a very shallow potential well at an internuclear equilibrium distance of about 2.7 Å the dissociation energy being very difficult to estimate. Interestingly, spin-orbit corrections are found to be necessary to get an adequate description of the metastable state of CuZn(2+), whereas relativistic corrections have no effects on neutral CuZn nor on CuZn(+).