Photodissociation measurements of bond dissociation energies: D-o(Al-2-Al), D-o(TiO+-Mn), and D-o(V-2(+)-V)

The bond dissociation energies D-0(Al-2-Al) = 2.701(5), D-0(TiO+-Mn) = 1.76 29(12), and D-0(V-2(+)-V) = 2.323(1) eV have been measured from the sudden onset of predissociation in the photodissociation spectra of Al-3. TiOMn+, and V-3(+). For Al-3, the predissociation threshold was observed in a spect rum arising from the metastable (4)A(2) state (in C-2v symmetry), and the v alue of D-0(Al-2-Al) = 2.701(5) eV was obtained by adding the energy of the (4)A(2) state to the measured predissociation threshold. For TiOMnt, there is currently no evidence that the predissociation threshold arises from a metastable excited electronic state; nor is there evidence that dissociatio n at the ground separated fragment limit fails to occur. Therefore, the pre dissociation threshold is taken to be the bond dissociation energy for this molecule. For V-3(+), the measured predissociation threshold occurs 0.32 e V above the collision-induced dissociation (CID) measurement. Based in part on a theoretically suggested (9)A(2)(") ground state for V-3(+) it is sugg ested that predissociation of V-3(+) occurs efficiently only after the V (3 d (4)4s(1), D-6(1/2)) + V-2(+) (X (4)Sigma (-)(g,1/2)) separated fragment l imit is exceeded in energy. Making a correction for the energy of this exci ted separated fragment limit then brings the photodissociation measurement into agreement with the CID result, and allows the bond energy to be determ ined as D-0(V-2(-)-V) = 2.323(1) eV. (C) 2001 Elsevier Science B.V.