The density profiles of particles of a dimerizing fluid in a slit formed by commensurate crystalline walls are studied, The pore walls consist of atoms located on the (100) plane of the face-centered cubic crystal lattice, The bulk fluid is treated using the formalism of Wertheim, The profiles are obtained in the PY1/APY approximation, The possibility of fluid particles forming a bond with the pore walls is included, The density in the center of a narrow pore is very heterogeneous due to dimerization and the orientation of the dimers with respect to the wall planes, Generally, the dimers are "expelled" from the adlayer, Expulsion from the adlayer leads to an increase in the density at the center of the pore, Complexes of fluid particles and wall atoms can form, These can be quite complex in the case of narrow pores.