Bond dissociation energies of diatomic transition metal selenides: TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe

Predissociation thresholds have been observed in the resonant two-photon ionization spectra of TiSe, ZrSe, HfSe, VSe, NbSe, and TaSe. It is argued that the sharp onset of predissociation corresponds to the bond dissociation energy in each of these molecules due to their high density of states as the ground separated atom limit is approached. The bond dissociation energies obtained are D₀(TiSe) = 3.998(6) eV, D₀(ZrSe) = 4.902(3) eV, D₀(HfSe) = 5.154(4) eV, D₀(VSe) = 3.884(3) eV, D₀(NbSe) = 4.834(3) eV, and D₀(TaSe) = 4.705(3) eV. Using these dissociation energies, the enthalpies of formation were found to be Δ_f,0KH^o(TiSe(g)) = 320.6 ± 16.8 kJ mol⁻¹, Δ_f,0KH^o(ZrSe(g)) = 371.1 ± 8.5 kJ mol⁻¹, Δ_f,0KH^o(HfSe(g)) = 356.1 ± 6.5 kJ mol⁻¹, Δ_f,0KH^o(VSe(g)) = 372.9 ± 8.1 kJ mol⁻¹, Δ_f,0KH^o(NbSe(g)) = 498.9 ± 8.1 kJ mol⁻¹, and Δ_f,0KH^o(TaSe(g)) = 562.9 ± 1.5 kJ mol⁻¹. Comparisons are made to previous work, when available. Also reported are calculated ground state electronic configurations and terms, dipole moments, vibrational frequencies, bond lengths, and bond dissociation energies for each molecule. A strong correlation of the measured bond dissociation energy with the radial expectation value, 'r'_nd, for the metal atom is found.