Reactions of Y⁺, Zr⁺, Nb⁺, and Mo⁺ with H₂, HD, and D₂

Abstract

Guided ion beam mass spectrometry is used to examine the kinetic energy dependence of reactions of the second row transition metal cations, Y + , Zr + , Nb + , and Mo + , with molecular hydrogen and its isotopologues. By using a meter long flow tube ion source, we are able to create Zr + , Nb + , and Mo + ions that are believed to be in their electronic ground state terms and primarily in the lowest spin-orbit levels and Y + mostly in its ground state. Corresponding state-specific reaction cross sections are obtained. Analysis of the cross section data yields 0 K bond dissociation energies of D 0 (Y + -H) ) 2.65 ( 0.08 eV, D 0 (Zr + -H) ) 2.26 ( 0.08 eV, D 0 (Nb + -H) ) 2.28 ( 0.07 eV, and D 0 (Mo + -H) ) 1.72 ( 0.06 eV. This thermochemistry is compared with theoretical calculations and previous experimental measurements. Results for the HD reactions indicate that Y + ( 3 D) reacts via a statistical mechanism, Zr + ( 4 F), Nb + ( 5 D), and Mo + ( 6 S) react via largely statistical mechanisms, and Y + ( 1 S) shows complex behavior. The reaction mechanisms and reactivity differences among these ions are explained by using simple molecular orbital concepts and by referring to potential energy surfaces calculated by Das and Balasubramanian. † Present address:

Activation of CH4 by Th+ as Studied by Guided Ion Beam Mass Spectrometry and Quantum Chemistry

“…A direct comparison of the thresholds from reaction 4 and 5 in Table 1 suggests that D 0 (Th + −CH 3 ) is 0.27 ± 0.22 eV larger than D 0 (Th + −H) and that D 0 (Th + −CD 3 ) is 0.12 ± 0.14 eV larger than D 0 (Th + −D), with a weighted average (after ZPE corrections) of 0.15 ± 0.12 eV. This is comparable to results for the transition metal congeners, Zr +15, 53 and Hf + , 25,69 where MCH 3 + and MH + BDEs are similar in strength, and to Ti + , 88 where the BDE for TiCH 3 + is stronger than that for TiH + by 0.2 ± 0.2 eV. Similar to the results for ThH + , theory overbinds by 0.4−0.9 eV, again, in part because of spin−orbit effects discussed below.…”

“…22,23,25,27,28,30,53,69,70,86 In all cases, the difference is attributed to competition with the formation of the metal carbene because of a shared, common intermediate. Because reactions of M + with H 2 produce only one product, no competition exists that may delay the onset of reaction.…”

Activation of CH4by Gas-Phase Mo+, and the Thermochemistry of Mo−ligand Complexes

“…The ions then undergo ∼10 5 collisions with He and ∼10 4 collisions with Ar in the meter-long flow tube before entering the guided ion beam apparatus. Results obtained previously 21 indicate that the Mo + ions produced in the DC/FT source are exclusively in their a 6 S ground state (less than 0.1% excited states). 47,48 and experimental work 49 has shown that endothermic cross sections can be modeled using eq 1 where σ 0 is an energy-independent scaling parameter, E is the relative translational energy of the reactants, E el is the average electronic energy of the reactants (0 in the present case), E 0 is the reaction threshold at 0 K, and n is a parameter that controls the shape of the cross section.…”

The most reactive third-row transition metal: Guided ion beam and theoretical studies of the activation of methane by Ir+

“…Generally, these conditions have been found to thermalize the ions, thereby producing atomic ions in their ground electronic state. For example, on the basis of comparisons to a surface ionization source, the DC/FT source was found to generate Sc + [34], Fe + [35], Co + [36], Ni + [37], Ru + [38], Rh + [38], and Pd + [38] ions with an average electronic temperature of 700 ± 400 K, and Y + , Zr + , Nb + , and Mo + ions with an average electronic temperature of 300 ± 100 K [39]. The populations of Ir + ions created under such conditions have been discussed in a previous paper [57], and rely on energies taken from spectroscopic work of Van Kleef and Metsch [40].…”