Photofragment spectroscopy and dynamics of NiOH+ and NiOH+(H2O)

Photodissociation of thermalized NiOH+ and NiOH+(H2O) are examined over the visible and near-ultraviolet using time-of-night mass spectrometry. Branch ing ratios and photodissociation cross sections are monitored as a function of laser wavelength. Loss of OH is the only dissociation channel observed in NiOH+, whereas loss of H2O and OH are present, and competitive, in the p hotodissociation of NiOH+(H2O). The photofragment spectrum of NiOH+ shows a bsorption bands at similar to 300 and similar to 400 nm. An almost identica l spectrum is observed for the net photodissociation of NiOH+(H2O). Spectro scopic thresholds taken from the photofragment spectra have been corrected to yield upper limits to the 0 K bond energies for the ions: D degrees (0)( Ni+-OH) less than or equal to 271 +/- 9 kJ/mol, D degrees (0)(NiOH+-H2O) le ss than or equal to 271 +/- 9 kJ/mol, and D degrees (0)(Ni+H2O-OH) less tha n or equal to 334 +/- 5 kJ/mol. Calculated B3LYP values are consistent with the experimental upper limits, but suggest that the true D degrees (0)(NiO H+-H2O) and D degrees (0)(Ni+H2O-OH) lie significantly below these upper li mits. Photodissociation of NiOH+(H2O) near 300 nm leads to greater OH produ ction than RRKM calculations predict, suggesting that excitation in this re gion leads to direct Ni+-OH bond cleavage.