Mass-analyzed threshold ionization of deuterium substituted indazole and benzimidazole and site-specific H/D exchange reaction

►The cation spectra of deuterium substituted indazole and benzimidazole have been recorded. ►The difference of the ionization energies of the deuterated species is found to be less than their un-deuterated molecules by only a few tens wavenumbers. ►Analysis of these experimental results suggests that the H/D exchange mainly takes place on the NH or CH sites of the five-membered ring of indazole and benzimidazole.