  Extreme nuclear deformations provide great insight into the geometric
formation of quantum many-body systems. In this work, the $4\alpha+2n$ linear
chain is assessed in $^{18}$O. We predict excitation energies,
moment-of-inertia, $\alpha$-, and $^{9}$Be-decay widths by using the
antisymmetrized molecular dynamics. We show that the $K^\pi=3^-$ linear-chain
states may be verified by the head-on $^{9}{\rm Be}+{}^{9}{\rm Be}$ collision
experiments.
