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Electronic spectroscopy and dissociation dynamics of cationic transition metal species
Solvation of transition metal ions plays an essential role in a wide variety of catalytic systems. However, a complete understanding of ion solvation requires looking within the bulk properties to examine the local environment around the metal ion. In the studies presented here, gas phase clusters produced through the electrospray process retain their nominal solution phase charge. By comparing the absorption properties of sequentially solvated metal ions in the gas phase to that in the bulk, the molecular chromophore is identified. Changing the type and number of solvent molecules around the metal center yields additional kinetic and dynamic information. Chapters 3 and 4 examine the photodissociation of the Ni2+(H 2O)n, Co2+(H2O)n, and Co2+(CH3OH)n (n = 4–7) species. The first spectroscopic observation of charge reduction was seen in the photodissociation of the n = 4 clusters to produce either H3O + or H+(CH3OH). A modest kinetic energy release implies a salt-bridge dissociation mechanism. For cobalt, photodissociation spectra of cluster ions with n = 6 and 7 are similar to those of cobalt (II) in solution, confirming the assignment of the 6-coordinate species as the chromophore in the solution phase. Results from these experiments led to the construction of a new apparatus devoted to electrospray (described in Chapter 2). As part of the electrospray process, NiOH+ and NiOH +(H2O) are formed by charge reduction. Similar ions are observed in the photodissociation of Ni2+(H2O) 4. Chapter 5 examines the photodissociation of thermalized NiOH + and NiOH+(H2O) in the visible and near ultraviolet. The photodissociation of NiOH+(H2O) exhibits competitive, nonstatistical photodissociation channels. Finally, Chapter 6 discusses the photodissociation spectrum of jet-cooled PtO+ from of 25,000 cm−1 to 30,000 cm −1. Excited state vibrational progressions are identified for 4Π−1/2 ← 4Σ3/2 and 4Π5/2 ← 4Σ 3/2 transitions and several vibrational peaks are rotationally resolved. Transitions arising from the 4Σ3/2 ground state show a spectroscopic onset of 25,520 cm−1, giving an upper limit to the bond strength of D0(Pt+-O) ≤ 305 kJ/mol. A hot band is observed at 25,317 cm−1 and rotational analysis predicts it to arise from a low-lying Ω = 7/2 state, probably 4Δ7/2.
Thompson, Christopher J, "Electronic spectroscopy and dissociation dynamics of cationic transition metal species" (2004). Doctoral Dissertations Available from Proquest. AAI3118336.