Retention of Bond Direction in Surface Reaction: A Comparative Study of Variously Aligned p‑Dihalobenzenes on Cu(110)

Previous studies indicated that the reagent bond direction of a bond being broken in surface reaction dominated the subsequent product recoil direction. Here we test this in an STM study of the electron-induced bond breaking for three clearly different alignments of each of two dihalobenzene reactions on Cu(110). A strong correlation was observed between the physisorbed adsorbate bond direction and the subsequent recoil direction of the chemisorbed halogen-atom product. The correlation was also evident in the theoretical modeling for the case of variously aligned diiodobenzene. The theory employed the impulsive two-state (I2S) approach to compute the reaction dynamics following electron attachment. This showed that the correlation between the prior bond direction and the subsequent product angular distribution was due to the directionality of the antibonding repulsion responsible for extending the molecule’s carbon–halogen bond, en route to reaction. Retention of bond direction in reaction dominated the effect of differing roughness of the surface along markedly different crystal axes.