Journal of Physical Chemistry A, Vol.104, No.44, 9901-9905, 2000
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. Branching 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 photodissociation of NiOH+(H2O). The photofragment spectrum of NiOH+ shows absorption bands at similar to 300 and similar to 400 nm. An almost identical spectrum is observed for the net photodissociation of NiOH+(H2O). Spectroscopic 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) less than or equal to 271 +/- 9 kJ/mol, and D degrees (0)(Ni+H2O-OH) less than 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)(NiOH+-H2O) and D degrees (0)(Ni+H2O-OH) lie significantly below these upper limits. Photodissociation of NiOH+(H2O) near 300 nm leads to greater OH production than RRKM calculations predict, suggesting that excitation in this region leads to direct Ni+-OH bond cleavage.