Schematic of the G323.18+0.15 complex before and after the collision. Panel a: long blueshifted cloud G323.18a comes from the northwestern direction and collides with G323.18b and G323.18c. Panels b and c: collision forms a U-shape structure and a dense layer. Panel d: YSOs are forming in the dense compressed layer, and then the strong stellar wind and radiation pressure blow away the sparse gas and dust between G323.18b and G323.18c.