Magnetic Circular Dichroism of C60+ and C60- Radicals in Argon Matrixes

Near-infrared transitions of the monoanion and monocation radicals of buckminsterfullerene isolated in argon matrixes (C60±/Ar) have been investigated using magnetic circular dichroism (MCD) and absorption spectroscopy, over the temperature range T = 1.6−30 K and magnetic-field range B = 0−4 T. Structure in the origin-band regions of both ions is partially attributed to the occupation of inequivalent matrix sites. The origin bands for the 2Hg ← 2Hu and 2Gg ← 2Hu transitions of C60+/Ar are nearly coincident, with the former at higher energy. The ground-state orbital angular momenta of both ions are quenched by crystal-field-stabilized Jahn−Teller (CF-JT) effects. Trapping is strong for C60-/Ar but weak for C60+/Ar. The transition from static to dynamic CF-JT effects for C60+/Ar gives rise to unusual temperature and magnetic-field dependencies of the MCD.