Observation of the lead carbonyls, PbnCO(n=1-4): reactions of lead atoms and small clusters with carbon monoxide in solid argon.

Reactions of laser-ablated Pb atoms with CO molecules in solid argon lead to the formation of the lead carbonyls, PbnCO (n=1-4), using matrix-isolation infrared spectroscopy. Absorption at 2027.7 cm(-1) is assigned to C-O stretching mode of the PbCO product, which appears and increases on annealing, disappears on broadband irradiation, and recovers on further annealing. Small lead cluster mono-carbonyls PbnCO (n=2-4) are also observed in the present infrared spectra. Based on the results of stepwise annealing and the comparison with theoretical predictions, the absorptions at 1915.5, 1923.8, and 2042.8 cm(-1) are assigned to Pb2CO, Pb3CO, and Pb4CO, respectively. Bridging CO is found in Pb2CO or Pb3CO, whereas terminal CO in Pb4CO. The density functional theory calculations have been performed on these molecules and small naked lead clusters. The good agreement between experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts provides strong support for the identifications of these lead mono-carbonyls PbnCO (n=1-4). Furthermore, energetic analysis for the possible reactions of lead atoms with CO molecules is also given.