Interstellar C 60
Buckminsterfullerene (C 60 ) has recently been detected through its infrared emission b ands in the interstellar medium (ISM), including in the proximity of massive stars, where physical condit ions could favor the formation of the cationic form, C +60. In addition, C+60was proposed as the carrier of two di ffuse interstellar bands in the near-IR, although a firm identi fica on still awaits gas-phase spectroscopic data. We examined in detail the Spitzer IRS spectra of the NGC 7023 reflection nebula, at a position cl se (7.5”) to the illuminating B star HD 200775, and found four previously unr eported bands at 6.4, 7.1, 8.2, and 10.5 μm, in addition to the classical bands attributed to polycylic aromatic hydrocarbons (PAHs ) and neutral C60 . These 4 bands are observed only in this region of the nebula, while C60 emission is still present slightly farther away from the sta r, and PAH emission even farther away. Based on this observation, on theoretical calculations we perform, and o laboratory studies, we attribute these bands to C +60. The detection of C + 60 confirms the idea that large carbon molecules exist in the gas ph e in these environments. In addition, the relative vari ation in the C60 and C+60 band intensities constitutes a potentially powerful probe f the physical conditions in highly UV-irradiated regions .