The ornamental design for a carbonationmechanism, as shown and described.
1. Carbonation mechanism
1.1 : Perspective (front, top, left)
1.2 : Front
1.3 : Back
1.4 : Right
1.5 : Left
1.6 : Top
1.7 : Bottom
The parts shown by means of broken lines in the reproductions are not part of the claimed design; the shadings in the reproductions represent contours only and do not illustrate an ornamentation or decoration on the surface of the product.
The broken lines in the drawings depict portions of the carbonation mechanism that form no part of the claimed design.