Electron spin resonance spectrum of CS –2 radical ion at 77°K

Abstract

CS^–₂ radical ions have been prepared by depositing sodium or potassium on solid carbon disulphide at 77°K in the rotating cryostat. The electron spin resonance (e.s.r.) spectrum of the CS^–₂ radical ion is similar to that of the analogous CO^–₂ radical ion which has been reported previously. The g-factor of the CS^–₂ radical ion exhibits a similar angular dependence to that of the CO^–₂ radical ion, but the shifts from the free spin value are considerably larger for CS^–₂. Hyperfine structure caused by interaction of the unpaired electron with naturally abundant carbon-13 nuclei has been observed in the spectrum of the CS^–₂ radical ion formed when sodium was deposited. The SĈS apex angle and the distribution of the unpaired electron over the radical anion have been calculated from the observed values of the carbon-13 hyperfine coupling constants and the g-factor. The SĈS angle in CS^–₂ is 141° which is larger than the OĈO angle of 121° in CO^–₂. However, the spin distribution is similar in both radical anions, being about 60 % on the central carbon atoms and 20 % on each of the terminal atoms.

There is a small hyperfine coupling to the alkali metal nucleus which shows that the unpaired electron is not completely transferred to the carbon disulphide molecule but is retained partially in the 3s orbital of the sodium or 4s orbital of the potassium. The unpaired spin densities in the alkali metal s-orbitals are smaller than the corresponding ones found for the CO^–₂ radical ion, showing that there is less interaction between the members of the ion-pair in the CS^–₂ radical ion.