We develop a theoretical framework for study of chemical dynamics induced by a scanning tunneling microscope. An analytically solvable limit of the expression derived for the reaction rate reveals the information content of the voltage dependence of the observable. The theory is applied to the problem of H-atom desorption from a silicon surface in the 4-10 V range, where desorption is triggered by a single electronic transition into a short-lived excited state localized on the H-Si bond. The resonance lifetime is extracted by fitting the numerical results to an observed desorption yield versus voltage curve [Foley , Phys. Rev. Lett. 80, 1336 (1998)].