Emission following UV laser photolysis of nickel carbonyl

Nickel tetracarbonyl in a moderate jet expansion was photolyzed with pulsed 193 and 248 nm light from an excimer laser. Ultraviolet and visible emission resulted from photolysis that also produced nickel atomic clusters. Emission intensity was recorded for 400 ns following the laser pulse over the wavelength range from 200 to 600 nm at better than 0.1 nm resolution. The complex emission spectrum consisted of 85 well-defined peaks from 200 to 472 nm, with many shoulders and overlapping peaks. Nickel atomic transitions were identified as the primary source of emission. Other peaks were tentatively identified as arising from either atmospheric contaminants, molecular fragment emission, or emission from nascent nickel atomic cluster formation.; Results are consistent with a two-photon excitation process retaining energy on the nickel atom throughout sequential CO loss at both wavelengths. A power dependence curve fitting procedure showed no evidence for more than one photochemical process or excited state for the 193 nm photolysis. Populations of nickel excited states were calculated. The highest energy nickel atomic states observed following photolysis (6.99 eV at 193 nm and 4.17 eV at 248 nm) were consistent with the 6.1 eV thermodynamic values for sum Ni-CO bond dissociation energies and indicated that published individual bond energy values are underestimated. These results are in accord with current understanding of the formation of nickel nanoparticles through nucleation of nickel atomic clusters in nickel carbonyl by collisions involving electronically excited nickel atoms.; Some emission peaks exhibited longer time decay than did the majority of peaks. No spectroscopic explanation for this difference is apparent in the group of nickel atomic transitions exhibiting this behavior. Rather the long time-duration is possibly the result of a postulated non-emitting slow channel for molecular fragment decay or part of a broader distribution not resolved in this experiment.; Laser power was controlled using a novel flowing gas attenuator cell containing N{dollar}sb2{dollar}O. The photochemistry of the attenuating primary absorption process and secondary NO excited state absorption were used to construct a model which well reproduced the transmission characteristics of the cell.