The Potential Energy Surface for Activation of Methane by Co+: An Experimental Study

Abstract

A guided-ion-beam mass spectrometer is used to study the reactions of Co+ + CD4 and CoCH2+ + D2 and thereby experimentally probe the potential energy surface for activation of methane by Co+. The results obtained are compared to recent theoretical results and agree with the conclusion that dehydrogenation of methane by Co+ is hindered by a tight four-center transition state complex. The major discrepancy observed between experiment and theory is in the height of this barrier, which theory predicts is 96-109 kJ/mol versus our experimental result of 34 ± 8 kJ/mol. The endothermicities of all reactions are measured and allow the determination of £>o(Co+-CD) = 422 ± 37 kJ/mol and Dq(Co+-C) = 347 ± 29 kJ/mol. We also find extensive hydrogen scrambling in the CoCH2+ + D2 reaction, a result that is interpreted by using phase space theory to help understand how various features on the potential energy surface control branching ratios among the various channels observed.

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

“…From Eq. (14), D 0 (D-CD 3 ) = 4.58 eV, and a calculated zero-point energy difference between IrD + and IrH + of 0.041 ± 0.004 eV, this predicts a threshold of 1.42 ± 0.06 eV for formation of IrD + in reaction (2). Our analysis of this cross section (Table 1) measures a somewhat higher threshold of 1.69 ± 0.07 eV.…”

“…Formation of IrD 2 + has the highest threshold of all processes observed, which is consistent with formation of the high-energy CD 2 neutral. The formation of MD 2 + product ions is unusual and has not been detected for reaction of methane with first-row [8][9][10][12][13][14][15]18], second-row [7,11,[16][17][18], and several thirdrow (La + , W + , Re + , Lu + ) transition metal ions [18,20,21]. However, this product has been observed in reactions of methane with Pt + [19].…”

“…Such ion beam studies also provide insight into the electronic requirements for the activation of methane by transition metal ions and periodic trends in this reactivity. We have applied this methodology to all the first-row and second-row transition metals except Tc [3,[7][8][9][10][11][12][13][14][15][16][17][18] and more recently to several of the third-row metals as well [18][19][20][21]. A significant advantage of these comprehensive studies is the comparison of bond energies and reactivities of all transition-metal complexes, thereby establishing periodic trends.…”

An ab initio study of the reaction mechanism of Co++NH3

“…There is a growing body of experimental information regarding the interactions of small neutral 1 and cationic [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] clusters of transition metals with compounds containing prototypical bonds ͑e.g., C-H, C-C, N-H, O-H, Si-H, Si-C͒ of importance in catalytic processes. Transition metal-main group complexes have been the focus of intense computational effort.…”

A Comprehensive Theoretical Study on the Reactions of Sc+ with CnH2n+2 (n=1–3): Structure, Mechanism, and Potential‐Energy Surface

“…Therefore, we believe that errors resulting from relativistic effects are much less than those due to incomplete basis sets and can be safely neglected. [51] and Co , [52] including detailed reaction mechanisms and PESs, were reported by Armentrout et al [11,12] They identified the four-centered TS shown in Scheme 1 (top). More recently, they also studied the reaction mechanism of Sc with CH 4 by using the CASSCF and MR-SDCI-CASSCF methods.…”