Crossed-Beam Study of Co+(3F4)+Propane: Experiment and Density Functional Theory

Abstract

A pulsed beam of Co+(3F4) crosses a pulsed beam of C3H8 or C3D8 gas under single collision conditions at collision energies of 0.01 eV and 0.21 eV. After a variable time delay t(ext) = 1-8 micros a fast high voltage pulse extracts product ions into a field-free flight tube for mass analysis. Consistent with earlier work, we observe prompt CoC3H6+ +H2 elimination products in 3:1 excess over CoC2H4+ +CH4 products at 0.21 eV on a 2-10 micros time scale. Long-lived CoC3H8+ complexes fragment predominantly back to Co+ +C3H8 reactants and to H2 elimination products on a 6-24 micros time scale. Density functional theory (B3LYP) calculations provide energies, geometries, and harmonic vibrational frequencies at key stationary points for use in a statistical rate model of the reaction. By adjusting two key multicenter transition state (MCTS) energies downward by 4-7 kcal mol(-1), we obtain good agreement with our decay time results and with the cross section versus collision energy of Armentrout and co-workers from 0.1-1.0 eV. B3LYP theory succeeds in finding relative energies of the MCTSs leading to CH4 and H2 in the proper order to explain the different product branching ratio for Co+ (which favors H2 over CH4) compared with its nearest neighbors Fe+ and Ni+ (which favor CH4 over H2).

Ethylene addition to Ru(CH2)(O)3 – A theoretical study

“…All relative energies discussed below relate to B3LYP/II/B3LYP/I calculations and include ZPE contributions. While the B3LYP functional used together with basis sets of triple-f quality can show errors in computed barrier heights as large as 4-7 kcal/mol [22] we found by comparison to CCSD(T)/II calibration data in earlier work [7] relative energies obtained at the B3LYP/ II//B3LYP/I level superior to relative energies directly obtained from B3LYP/I calculations. Our present results are consistent and directly comparable with our previously published data in [6], but please note that a different basis set was used in our first report [8] on the reactivity of OsO 3 (CH 2 ) against ethylene.…”

Propane activation by MC5H+5 (M=Ni and Co): An experimental and theoretical work

“…In a successive work Weisshaar et al [21] confirmed the same mechanism for the reaction of Co + with propane. According to the previously described level of theory the lowest energy state of Ni(C 5 H 5 ) + is the triplet state, which is 21.4 kJ/mol lower than the singlet state.…”

“…Reactions of bare transition metal ions with hydrocarbons received much attention [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] and several aspects of their reactivity have been clarified, even with the aid of accurate theoretical calculations [19][20][21]. Much less extensive is our knowledge about the reactivity of ligated metal ions, although it is well known that the presence of a ligand influences the reactivity of a metal ion [22].…”

Velocity map imaging of ion-molecule reaction products: Co+(3F4)+isobutane

“…29 In particular, B3LYP consistently finds that the lowest-energy pathways to elimination products involve concerted passage over rate-limiting multicenter transition states ͑MCTS͒, rather than initial CC or CH bond insertion and stepwise rearrangement as previously supposed. 10,15,16,19,26,28 In earlier work, we combined pulsed, crossed-beam methods and pulsed, time-of-flight mass spectrometry ͑TOF-MS͒ to study M ϩ ϩalkane reactions for which reactant electronic state and collision energy were carefully controlled. 16,19,20,26,28 Preparation of M ϩ by resonant twophoton ionization ͑R2PI͒ using ns dye lasers allowed us to monitor the evolution of long-lived M͑alkane) ϩ complexes to H 2 or CH 4 elimination products in real time with sub-s time resolution.…”

“…10,15,16,19,26,28 In earlier work, we combined pulsed, crossed-beam methods and pulsed, time-of-flight mass spectrometry ͑TOF-MS͒ to study M ϩ ϩalkane reactions for which reactant electronic state and collision energy were carefully controlled. 16,19,20,26,28 Preparation of M ϩ by resonant twophoton ionization ͑R2PI͒ using ns dye lasers allowed us to monitor the evolution of long-lived M͑alkane) ϩ complexes to H 2 or CH 4 elimination products in real time with sub-s time resolution. We modeled the outcome of such measurements by applying B3LYP theory to stationary points along the lowest-energy reaction path and using statistical rate theory ͑RRKM theory with conservation of total angular momentum͒ [30][31][32] to compute experimental quantities.…”