Photoionization Study of Fe(CO)₅ and Ni(CO)₄

Area of Science:

• Physical Chemistry
• Atomic and Molecular Physics
• Mass Spectrometry

Background:

• Metal carbonyls are important in catalysis and materials science.
• Understanding their photoionization fragmentation is crucial for chemical dynamics.
• Previous studies using electron impact have provided some insights.

Purpose of the Study:

• To investigate the photoionization yield curves and ionization thresholds of iron pentacarbonyl and nickel tetracarbonyl.
• To elucidate the ionization-fragmentation processes of these metal carbonyls under photon impact.
• To compare experimental results with thermochemical data and electron impact methods.

Main Methods:

• Photoionization mass spectrometry was used to obtain yield curves from onset to 600Å.
• Ionization threshold values were determined for fragment ions, including metal cations (Fe+, Ni+) and CO+.
• Appearance potentials and heats of formation were calculated and compared with thermochemical data.

Main Results:

• Photoionization yield curves and ionization thresholds were established for fragment ions of Fe(CO)5 and Ni(CO)4.
• Experimental appearance potentials and heats of formation for metal ions closely matched thermochemical calculations (within 0.1 eV).
• The average bond dissociation energy agreed well with thermochemical values (within 0.02 eV), and kinetic shifts were minimal for Fe+ and Ni+ formation.

Conclusions:

• Photon impact provides detailed information on the ionization-fragmentation of metal carbonyls.
• The close agreement between experimental and thermochemical data validates the methods used.
• Nickel ions are likely formed directly from the parent molecule ion, not through cascade fragmentation.