Journal of Physical Chemistry A, Vol.117, No.6, 1102-1109, 2013
Electron Attachment to Fe(CO)(n) (n=0-5)
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) x 10(-8) cm(3) at s(-1) 300 K and (8.8 +/- 2) x 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) x 10(-8) cm(3) s(-1) with an upper to branching fraction of 0.5 to yield Fe(CO)(4), indicating that significant fragmentation to smaller Fe(CO)(n) occurs.