Electron Attachment to Fe(CO)_n (n = 0–5)

Abstract

The rate constants of thermal electron attachment at 300 and 400 K to Fe(CO)(n) (n = 0-5) have been measured using a flowing afterglow Langmuir probe apparatus. The stable species Fe(CO)(5) was studied using the traditional method of monitoring electron depletion as a function of reaction time, and the remaining short-lived species were studied using the variable electron and neutral density attachment mass spectrometry (VENDAMS) technique. Attachment to Fe(CO)(5) is purely dissociative and about 20% efficient with a rate constant of (7.9 ± 1.4) × 10(-8) cm(3) s(-1) at 300 K and (8.8 ± 2) × 10(-8) cm(3) s(-1) at 400 K. The attachment rate constants decrease significantly as each CO ligand is removed, with Fe(CO)(n) (n = 4 to 1) attaching with efficiencies on the order of 10%, 1%, 0.1%, and 0.01% respectively. Under the conditions here, attachment to Fe(CO)(4) and Fe(CO)(3) are likely entirely dissociative, whereas attachment to Fe(CO)(2) and Fe(CO) are almost entirely associative. A statistical kinetic modeling approach is used to explain the strong dependence of the attachment rate constant on the number of ligands present in the neutral species through a combination of increasing autodetachment rates and decreasing exothermicities to dissociative attachment. The VENDAMS data also define the 300 K mutual neutralization rate constant of Fe(CO)(4)(-) + Ar(+) to be (5.0 ± 0.8) × 10(-8) cm(3) s(-1) with an upper limit to branching fraction of 0.5 to yield Fe(CO)(4), indicating that significant fragmentation to smaller Fe(CO)(n) occurs.

Kinetics of electron attachment to SF3CN, SF3C6F5, and SF3 and mutual neutralization of Ar+ with CN− and C6F5−

“…3,4 The SF 3 electron attachment rate constant [ Fig. The method has been described in detail elsewhere.…”

“…[1][2][3][4] VENDAMS yields measurements of electron attachment to short-lived radical species and neutral product distributions of ion-ion mutual neutralization, accurate mutual neutralization rate constants, as well as providing evidence for a new ternary mechanism for ion-ion mutual neutralization, 5 and dubbed electron catalyzed mutual neutralization (ECMN). [1][2][3][4] VENDAMS yields measurements of electron attachment to short-lived radical species and neutral product distributions of ion-ion mutual neutralization, accurate mutual neutralization rate constants, as well as providing evidence for a new ternary mechanism for ion-ion mutual neutralization, 5 and dubbed electron catalyzed mutual neutralization (ECMN).…”

“…[1][2][3][4] VENDAMS yields measurements of electron attachment to short-lived radical species and neutral product distributions of ion-ion mutual neutralization, accurate mutual neutralization rate constants, as well as providing evidence for a new ternary mechanism for ion-ion mutual neutralization, 5 and dubbed electron catalyzed mutual neutralization (ECMN). 3 To date, the most comprehensive study has been with a series of neutrals that form SF n − after attachment of an appropriate neutral precursor, e.g., SF 6 − from SF 6 , SF 5 − from SF 5 Cl and SF 5 C 6 H 6 , and SF 4 − from SF 4 . Dissociative electron attachment to a closed shell species yields a neutral radical fragment and an anion, serving as a source of both those types of species.…”

“…While flowing afterglow Langmuir probe (FALP) apparatuses have commonly been used to measure electron attachment rate constants by introducing neutral species to a weakly ionized thermal plasma, 6 VENDAMS exploits the presence of the products of electron attachment to those neutrals. 4 In studying these systems, we have been able to derive attachment kinetics to SF 5 , SF 3 , and SF 2 , although the latter two with large uncertainties. By varying the initial electron density of the afterglow N e (0) over a wide range (1 × 10 8 to 5 × 10 10 e − /cm 3 ) and measuring relative ion intensities at the end of the flow tube, it is possible to decipher the kinetics involving these product fragments.…”

“…One of the weak links in that study was that the electron attachment rate to SF 3 had over an order of magnitude uncertainty, which propagated to other measurements, primarily the product distribution of mutual neutralization (MN) of SF 4 − and Ar + . One of the weak links in that study was that the electron attachment rate to SF 3 had over an order of magnitude uncertainty, which propagated to other measurements, primarily the product distribution of mutual neutralization (MN) of SF 4 − and Ar + .…”