Stable isomers, transition states, and their photoabsorption spectra for the Na-4(+) cluster are determined by ab initio MRCI calculations. Three stable geometries of symmetry C-2v, D-2h, and D-2d and two transition states of symmetry C-s and C-2 are identified. The D-2d configuration is a new geometry not previously obtained in ab initio calculations. The photoabsorption spectra of the three isomers and the transition states are used to interpret experimental absorption data. Dissociation dynamics and possible laser control of isomer populations are discussed in terms of the electronic states of the cluster.