By exposing precursor molecules traveling in a molecular beam to a narrow bandwidth laser beam (hu) tuned to a vibrational resonance frequency of the molecules and aimed orthogonal to the molecular beam (FIG. 6A), only those molecules having velocity (va) along trajectory (A) orthogonal to the laser beam are excited, becoming several orders of magnitude more reactive, affording a high degree of control over precise locations of reactions of molecules. Controlling a reaction on a surface of a solid substrate, includes; (a) obtaining a precursor molecule that includes (or can be reacted to form) species to be reacted with the substrate; (b) creating a molecular beam (eg., supersonic) that includes the precursor molecule; (c) vibrationally exciting the molecule with the laser beam tuned to a vibrational resonance frequency of the molecule; and (d) causing the exciting molecule to impinge on the substrate, enabling reactions (deposition, etching . . . ) of the species with the substrate.