A Bijection between Atomic Partitions and Unsplitable Partitions

In the study of the algebra $\mathrm{N}\mathrm{C}\mathrm{S}\mathrm{y}\mathrm{m}$ of symmetric functions in noncommutative variables, Bergeron and Zabrocki found a free generating set consisting of power sum symmetric functions indexed by atomic partitions. On the other hand, Bergeron, Reutenauer, Rosas, and Zabrocki studied another free generating set of $\mathrm{N}\mathrm{C}\mathrm{S}\mathrm{y}\mathrm{m}$ consisting of monomial symmetric functions indexed by unsplitable partitions. Can and Sagan raised the question of finding a bijection between atomic partitions and unsplitable partitions. In this paper, we provide such a bijection.