Chiral-Selective Chemistry Induced by Spin-Polarized Secondary Electrons from a Magnetic Substrate

We demonstrate for the first time that low-energy spin-polarized secondary electrons, produced by irradiation of a magnetic substrate, can induce chiral-selective chemistry. Our approach was to perform detailed measurements of the reaction rate for x-ray induced, secondary electron photolysis of a model chiral compound, ($R$)- or ($S$)-2-butanol, adsorbed on a magnetized Permalloy substrate. The results showed that there is an enhancement of $\sim 10\%$ in the rate of CO bond cleavage that depends on the chirality of the molecule and the spin polarization of the substrate secondary electrons.

Figure 1

C 1 s XPS spectrum of ($R$)-2-butanol adsorbed on Permalloy at 90 K obtained at the start of a photolysis series. The points are the raw data; the dashed lines are the individual fitted components, and the solid line is the synthesized curve. The filled-in region represents the C-O peak, which directly probes the chiral carbon. Also shown are models of ($S$)- and ($R$)-2-butanol.

Figure 2

Series of C 1 s XPS spectra of ($R$)-2-butanol adsorbed on Permalloy obtained sequentially while irradiating with 1190-eV x rays. The inset shows the area of the C-O peak as a function of irradiation time (data points), and the solid line is the curve resulting from least-squares fitting of a single exponential peak [$A+B\exp (-t/\tau )$] to the data.

Figure 3

Summary of the time constant results. The squares are the points for $+$ magnetization, and the circles are the points for $-$ magnetization. The lines represent the average values, which are also tabulated: (a) ($S$)-2-butanol and (b) ($R$)-2-butanol.