Electronic effects in carbon-hydrogen and carbon-carbon bond activation: reactions of excited-state chromium(+) with propane, butane, methylpropane, and dimethylpropane

Abstract

Guided ion beam mass spectrometry is used to study the reactions of excited states of Cr{sup +} with propane, butane, methylpropane, and dimethylpropane. The effect of electronic energy as well as kinetic energy on the reactivity of atomic chromium ions is examined and reveals several interesting aspects of Cr{sup +} chemistry. The present results include the first direct evidence for reaction of the Cr{sup +}({sup 6}D) first excited state. Most interesting is the observation that the excited quartet states of Cr{sup +} react with alkanes very differently than ground-state Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 6}S). Previously we found that Cr{sup +}({sup 6}S) activates only C-C bonds of alkanes, while in the present study we find that the excited Cr{sup +}({sup 4}d, {sup 4}g) states activates both C-H and C-C bonds of alkanes. The reactivity of the {sup 6}D first excited state of Cr{sup +} is similar to that of the {sup 6}S ground state. These reaction systems are currently the only examples where electronic excitation of a transition-metal ion drastically changes the products formed. 32 refs., 4 figs., 5 tabs.