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Resonant three-photon ionization spectroscopy has been used to study the late 4d and 5d transition metal carbides RuC, RhC, OsC, IrC, and PtC. These species, like most diatomic transition metals with open nd subshells, exhibit an exceptionally high density of states near the ground separated atom limit. Spin-orbit and nonadiabatic interactions provide a means for the molecules to rapidly dissociate as soon as the bond dissociation energy (BDE) is exceeded. The result is a sharp predissociation threshold that is identified as the BDE. The high BDEs of these five molecules required the use of two tunable lasers to reach the BDE. Measured values of D0(RuC) = 6.312(2) eV, D0(RhC) = 6.007(2) eV, D0(OsC) = 6.427(2) eV, D0(IrC) = 6.404(2) eV, and D0(PtC) = 6.260(2) eV were obtained, where the value is parentheses represents the estimated error limit in units of the last quoted digit. A new electronic state of PtC, tentatively assigned as the c(_^3)Σ_1^+ state, has been found with T0 = 22442 cm-1. These BDEs are combined with recently measured ionization energies to obtain BDEs of the associated cations. Electronic structure calculations are also reported to investigate the chemical bonding in more detail. Trends in the BDEs of the diatomic transition metal carbides are also discussed.
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Bond dissociation energies of diatomic transition metal nitrides
Resonant two-photon ionization (R2PI) spectroscopy has been used to measure the bond dissociation energies (BDEs) of the diatomic transition metal nitrides ScN, TiN, YN, MoN, RuN, RhN, HfN, OsN, and IrN. Of these, the BDEs of only TiN and HfN had been previously measured. Due to the many ways electrons can be distributed among the d orbitals, these molecules possess an extremely high density of electronic states near the ground separated atom limit. Spin–orbit and nonadiabatic interactions couple these states quite effectively, so that the molecules readily find a path to dissociation when excited above the ground separated atom limit. The result is a sharp drop in ion signal in the R2PI spectrum when the molecule is excited above this limit, allowing the BDE to be readily measured. Using this method, the values D0(ScN) = 3.905(29) eV, D0(TiN) = 5.000(19) eV, D0(YN) = 4.125(24) eV, D0(MoN) = 5.220(4) eV, D0(RuN) = 4.905(3) eV, D0(RhN) = 3.659(32) eV, D0(HfN) = 5.374(4) eV, D0(OsN) = 5.732(3) eV, and D0(IrN) = 5.115(4) eV are obtained. To support the experimental findings, ab initio coupled-cluster calculations extrapolated to the complete basis set limit (CBS) were performed. With a semiempirical correction for spin–orbit effects, these coupled-cluster single double triple-CBS calculations give a mean absolute deviation from the experimental BDE values of 0.20 eV. A discussion of the periodic trends, summaries of previous work, and comparisons to isoelectronic species is also provided.
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- Award ID(s):
- 1952924
- PAR ID:
- 10399162
- Publisher / Repository:
- American Institute of Physics
- Date Published:
- Journal Name:
- The Journal of Chemical Physics
- Volume:
- 158
- Issue:
- 8
- ISSN:
- 0021-9606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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