Professor Michael Morse recently contributed his research "Bond dissociation energies
of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi" to The Journal of Chemical Physics, developing a method of determining bond dissociation energies for transition metal
silicides in order to both advance computation efforts and our understanding of chemical
bonding in general. A press release distributed by AIP Publishing relates the following:
“What I’m so pleased about with this new technique that we’ve developed is that it’s not just applicable to a small set of molecules,” said Michael Morse, one of the work’s authors. “It’s based on the fact that these small transition metal molecules have a density of electronic states that increases very rapidly as you get close to the dissociation limit, and that’s key in causing the molecule to fall apart as soon as you get above that limit […] The peculiarities of the transition metals make the method broadly applicable to that entire class of molecules, which are quite difficult to investigate by other means.”
To read the full press release, click here.
Predissociation thresholds have been observed in the resonant two-photon ionization
spectra of TiSi, ZrSi, HfSi, VSi, NbSi, and TaSi. It is argued that because of the
high density of electronic states at the ground separated atom limit in these molecules,
the predissociation threshold in each case corresponds to the thermochemical bond
dissociation energy. The resulting bond dissociation energies are D0(TiSi) = 2.201(3) eV, D0(ZrSi) = 2.950(3) eV, D0(HfSi) = 2.871(3) eV, D0(VSi) = 2.234(3) eV, D0(NbSi) = 3.080(3) eV, and D0(TaSi) = 2.999(3) eV. The enthalpies of formation were also calculated as Δf,0KH°(TiSi(g)) = 705(19) kJ mol−1, Δf,0KH°(ZrSi(g)) = 770(12) kJ mol−1, Δf,0KH°(HfSi(g)) = 787(10) kJ mol−1, Δf,0KH°(VSi(g)) = 743(11) kJ mol−1, Δf,0KH°(NbSi(g)) = 879(11) kJ mol−1, and Δf,0KH°(TaSi(g)) = 938(8) kJ mol−1. Using thermochemical cycles, ionization energies of IE(TiSi) = 6.49(17) eV and IE(VSi)
= 6.61(15) eV and bond dissociation energies of the ZrSi−and NbSi− anions, D0(Zr–Si−) ≤ 3.149(15) eV, D0(Zr−–Si) ≤ 4.108(20) eV, D0(Nb–Si−) ≤ 3.525(31) eV, and D0(Nb−–Si) ≤ 4.017(39) eV, have also been obtained. Calculations on the possible low-lying
electronic states of each species are also reported.
To read the full published text, click here.