Iron isotope fractionation between liquid and vapor phases of iron pentacarbonyl

Abstract

Iron isotope fractionation between liquid and vapor iron pentacarbonyl was measured in a closed system at ∼0 and ∼21 °C to determine if Fe isotope analysis of iron pentacarbonyl vapor is viable using electron-impact, gas-source mass spectrometry. At the 2 σ level, there is no significant Fe isotope fractionation between vapor and liquid under conditions thought to reflect equilibrium. Experiments at ∼0 °C indicate iron pentacarbonyl vapor is ∼0.05 per mil (‰) greater in 56Fe/ 54Fe than liquid iron pentacarbonyl, which is just resolvable at the 1 σ level. Partial decomposition of iron pentacarbonyl vapor or liquid to an iron oxide or iron metal shows that significant isotopic fractionation occurs, where the decomposed product has a lower 56Fe/ 54Fe ratio as compared to the starting iron pentacarbonyl. It follows that methods to decompose iron pentacarbonyl must be quantitative to obtain accurate isotope values.