Selectively breaking the O–H bond in HOD

Vibrationally mediated photodissociation of HOD, in which one photon excites an O–H stretching vibration and another photon dissociates the vibrationally excited molecule, preferentially breaks the O–H bond for some photolysis wavelengths. Excitation of the third O–H stretching overtone (4νOH ) of HOD followed by photolysis with a 239.5 or 266 nm photon produces at least 15 times more OD than OH product, as determined by laser induced fluorescence detection of both species. Dissociation of HOD(4νOH ) with a 218.5 nm photon produces comparable amounts of OH and OD fragments. This large selectivity and strong dependence on the wavelength of the photolysis photon is consistent with qualitative models of vibrationally mediated photodissociation and with recent calculations.