Assignment of the Lowest Excited States of C₇₀ and Evidence for Fluorescence from the S₂ State

Abstract

Highly structured fluorescence, phosphorescence, and fluorescence−excitation spectra of C70 in neon matrixes are reported. Fluorescence from both S1 and S2 states is observed, and these are identified as being of A2‘ and E1‘ symmetry and have gas-phase energies estimated at 15 560 and 15 725 cm-1, respectively. A third singlet state is identified in the excitation spectrum and is proposed to be of A2‘‘ symmetry with an estimated gas-phase energy of 16 000 cm-1. Finally, the phosphorescence is dominated by vibrational bands of e1‘ symmetry pointing to the lowest triplet state of A2‘ symmetry. Its energy lies at 12 588 cm-1 above that of the ground state in the neon matrix. From a comparison with data from the literature, the existence of a second triplet state of E1‘ character is inferred, which lies about 165 cm-1 above the lowest triplet state, i.e., with the same energy separation as the lowest two singlet states.