Photolytic Decomposition of Hydrogenated C70: C70H38 and C70D38

Abstract

The hydrogenated C70 fullerenes C70H38 and C70D38 have been photolyzed at 245 nm under Ar or He flow. The photolysis rate constant have been measured: k = 1.54×10−3 s−1 for C70H38, and the photolysis of C70D38 occurs at a rate of 1.17×10−3 s−1. A remarkable isotope effect in the photolysis of the two molecules has been determined kH/kD = 1.32. The photolysis mechanism and products of C70H38 and C70D38 have been discussed and, based on the isotope effect, the rate determining step involves, as for other fulleranes, the activation of the C‐H and C‐D bond. The UV photons cause the dehydrogenation of C70H38 and C70D38 and their oligomerization. In an astrochemical context the photolysis reaction of C70H38 should produce back C70 with release of molecular hydrogen. The role of fulleranes and hydrogenated carbon with fullerene‐like structure in space has been briefly discussed. C70H38 thermally treated at 600°C under N2 releases H2 forming back C70, which was easily recognized from its characteristic FT‐IR spectrum. The reaction is not fully reversible, and carbonaceous matter is formed as secondary product. The molar extinction coefficient of C70H38 and C70D38 has been determined in n‐hexane at 214 nm, the maximum of absorption of these two molecules; ε214 = 6300 L cm−1 mol−1 for the former and ε214 = 5800 L cm−1 mol−1 for the deuterated fullerane.