Hydroxyl radical production techniques

Robert. C. Ekey and Elizabeth F. McCormack, Bryn Mawr College

As a first step to better understand the effects of electronic and nuclear angular momentum on the ionization mechanisms in transient diatomic molecules, multiple methods for producing the hydroxyl radical, OH, in situ were explored. OH is of interest because the lowest energy ionic singlet and triplet states interact and can cause complex resonances to occur in the energy region of the ionization threshold. These complex resonances can be probed by first populating the, D or 3 state via a two-photon transition from the ground, X, state of OH, and then exciting from there to the states of interest. Three liquids were used as the parent molecule for the OH, formic acid (HCO-OH), Hydrogen peroxide H2O2 and water, H2O. In each case, to create the sample the liquid was vaporized and entrained in a molecular beam. To produce the OH, the formic acid and hydrogen peroxide can be photodissociated using laser light; the water can be dissociated by sending a high current through the vapor using a discharge source situated at the source of the molecular beam. Entrained helium and argon were found to increase OH production. Time of flight mass spectrometry was used to detect ions directly produced by these production processes, and was also used to detect ions produced by resonant enhanced multi-photon ionization (REMPI) of neutral OH giving an indication of the amount of OH produced.