Permutational symmetry, isotope effects, side crossing, and singlet-triplet splitting in anthracene·He_N (N=1, 2) clusters

Quantum-mechanical calculations for the energetics, nuclear dynamics, and electronic-vibrational spectorscopy of An·⁴He_N and An·³He₁ clusters in the ground (S₀) and in the first spin-allowed excited (S₁) electronic state are presented. As such, the isotope effects and the implications of permutation symmetry on the nuclear level structure are explored. In the context of electronic-vibrational level structure, novel information is obtained on spectral shifts and Franck-Condon factors for the S₀→S₁ tranition in the An·⁴He_N and An·³He_N quantum clusters.