Direct Determination of the Ionization Energies of PtC, PtO, and PtO2 with VUVRadiation

Journal Article · Mon Jul 21 04:00:00 EDT 2008 · The Journal of Physical Chemistry A

OSTI ID:943969

Citir, Murat; Metz, Ricardo B; Belau, Leonid; Ahmed, Musahid

Photoionization efficiency curves were measured for gas-phase PtC, PtO, and PtO2 using tunable vacuum ultraviolet (VUV) radiation at the Advanced Light Source. The molecules were prepared by laser ablation of a platinum tube, followed by reaction with CH4 or N2O and supersonic expansion. These measurements providethe first directly measured ionization energy for PtC, IE(PtC) = 9.45 +- 0.05 eV. The direct measurement also gives greatly improved ionization energies for the platinum oxides, IE(PtO) = 10.0 +- 0.1 eV and IE(PtO2) = 11.35 +- 0.05 eV. The ionization energy connects the dissociation energies of the neutral and cation, leading to greatly improved 0 K bond dissociation energies for the neutrals: D0(Pt-C) = 5.95 +- 0.07 eV, D0(Pt-O)= 4.30 +- 0.12 eV, and D0(OPt-O) = 4.41 +- 0.13 eV, as well as enthalpies of formation for the gas-phase molecules Delta H0 f,0(PtC(g)) = 701 +- 7 kJ/mol, Delta H0f,0(PtO(g)) = 396 +- 12 kJ/mol, and Delta H0f,0(PtO2(g)) = 218 +- 11 kJ/mol. Much of the error in previous Knudsen cell measurements of platinum oxide bond dissociation energies is due to the use of thermodynamic second law extrapolations. Third law values calculated using statistical mechanical thermodynamic functions are in much better agreement with values obtained from ionization energies and ion energetics. These experiments demonstrate that laser ablation production with direct VUV ionization measurements is a versatile tool to measure ionization energies and bond dissociation energies for catalytically interesting species such as metal oxides and carbides.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: Chemical Sciences Division
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 943969
• Report Number(s): LBNL-1231E
• Journal Information: The Journal of Physical Chemistry A, Journal Name: The Journal of Physical Chemistry A Vol. 112
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABLATION
ADVANCED LIGHT SOURCE
CARBIDES
DISSOCIATION
Direct Determination
Ionization Energies
EFFICIENCY
IONIZATION
LASERS
OXIDES
PHOTOIONIZATION
PLATINUM
PLATINUM OXIDES
PRODUCTION
RADIATIONS
THERMODYNAMICS