A beam of Ni+(D-2(5/2)) is formed at a sharp zero of time by resonant two-photon ionization with a nanosecond dye laser pulse and crossed with a beam of n-butane-h(10) or n-butane-d(10) gas. The ion-molecule reaction occurs under single-collision conditions in field-free space in the extraction region of a time-of-flight mass spectrometer, After a variable time delay t(ext) = 0.5-8 mu s, a fast high-voltage pulse extracts product ions and residual reactant ions into a field-free flight tube for mass analysis. Analysis of the metastable decay of NiC4H10+ complexes from tailing of fragment ion peaks and from retarding field separation reveals detailed information about the formation of elimination products (primarily ethane and H-2) and the decay back to Ni+ reactants in different time windows from 0.2 to 25 mu s after initiation of the collision. To understand the data, we have used density functional theory in its B3LYP variant to locate and characterize the geometries, potential energies, and vibrational frequencies of some 25 stationary points on the ground-state doublet potential energy surface for Ni+ + n-C4H10. As in earlier work on Ni+ + C3H8, we find that the highest potential energy points along pathways leading to H-2, CH4, and C2H6 elimination are multi-center transition states (MCTSs) involving simultaneous motion of many atoms about the Ni+ center. The extensive body of information from the electronic structure calculations provides realistic input to a statistical (RRKM) rate model of the reaction. Many details of the rime evolution of long-lived complexes for both NiC4H10+ and NiC4D10+ can be understood semiquantitatively when conservation of angular momentum is accounted for in approximate fashion. In our best model, the energetics of the MCTSs leading to C2H6 and H-2 elimination must be adjusted downward by 2-3 and 7 kcal/mol, respectively, from the calculated barrier heights. According to this model, essentially all of the C2H6 and H-2 products come from initial insertion of Ni+ into the central CC bond, the weakest bond in the alkane. The lowest energy path to H-2 elimination is novel, involving initial insertion into the central CC bond followed by simultaneous migration of two beta-hydrogens toward each other while being stabilized by the metal cation center. Insertion into a terminal CG bond or into either type of CH bond leads to substantially higher energy MCTSs that are likely unimportant at low collision energy.