The Electronic Spectrum and Structure of Tetrasulfur Dinitride

Ab initio configuration interaction calculations of the ground and singlet A' and A " excited states have been performed, with all possible single and double excitations from the 10 highest occupied orbitals to the lowest 17 virtual Orbitals being included, the previous C s symmetry molecular structure being used. Some of the states can be identified with excitation f rom individual occupied (SCF) orbitals to members of the virtual set, but some are not well represented by single configuration concepts. The results suggest that the three broad UV-spectral maxima observed in solution are not single excitations, but groups of excited states, with a total of 8 states. The closeness of some of these states makes positive assignment difficult. The most probable assignment is 455 nm (1 A"), 377 nm (2A" + 1 A' + 2A'), ~ 277 nm (3A" + 3A'), 232 nm (4A' + 4A").