Negative Ions from Metal Carbonyls by Electron Impact*

Interactions of low-energy electrons with the FEBID precursor chromium hexacarbonyl (Cr(CO)6)

“…In contrast to W(CO) 6 [ 13 ], the series of CO loss is complete in the present case, with the formation of the bare metal anion. This is in agreement with Pignataro et al [ 20 ], where the six anionic species where reported. The corresponding anion yields indicate that the number of leaving CO ligands increases with the electron energy.…”

“…The excess electron should occupy the lowest unoccupied molecular orbital (LUMO) 9a 1g with sigma character [ 19 ], or one of the higher-lying virtual molecular orbitals. The ion yields for the detected anionic species are in agreement with Pignataro and co-workers [ 20 ]. The dissociative channels described in this study follow the reactions below:…”

“…In Table 1 appearance energies and peak positions are listed and compared with the results from Pignataro and co-workers. The appearance energies are in good agreement, and the maximum deviation from the previous values is 0.45 eV for Cr − formation [ 20 ].…”

“…Electronic energy levels of metal carbonyls and metal cyanides were described by Gray and Beach [ 18 ], and the molecular orbitals were calculated by Johnson and Klemperer using the SCF-Xα-MSW method [ 19 ]. Negative ions were previously reported for a series of pentacarbonyl metals of group VI in the periodic table including Fe(CO) 5 , showing dissociation by capture of LEE with an energy close to 0 eV [ 20 ]. Electron ionization of W(CO) 6 clusters was also recently investigated [ 21 ] showing the sequential decay of the ionized organometallic precursor.…”

Low-energy electron interaction and focused electron beam-induced deposition of molybdenum hexacarbonyl (Mo(CO)6)

“…For Mo(CO) 6 , the precursor of interest in this study, dissociative electron-capture experiments were reported in the mid-1970s by Winters et al [ 19 ], where the peak positions of negative ions formed through sequential CO loss from one up to four carbonyl groups were reported. Pignataro et al [ 20 ] also published the energy dependence of the same fragment formation from about 0 eV up to about 10 eV and George et al [ 21 ] determined the rate constant for the formation of [Mo(CO) 5 ] − and found it to be 1.3 × 10 −7 cm 3 ·molecule −1 ·s −1 . This is a very high rate constant, which is consistent with cross section measurements for single-ligand loss in DEA to Co(CO) 3 NO [ 25 ] and Pt(PF 3 ) 4 [ 26 ], which were found to be 4.1 × 10 −16 cm 2 and 1.98 × 10 −16 cm 2 , respectively, that is, only about a factor of 10 below the πλ 2 , s-wave attachment cross section given by the respective DeBroglie wavelength [ 26 – 27 ].…”