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The structure, bonding, electron distribution, normal mode frequencies and the corresponding vibrational assignments of tetrarsenic tetrasulfide (As4S4) in D2d symmetry are examined theoretically using the gaussian 98 set of quantum chemistry codes at the HF, MP2 and B3LYP(DFT) levels of theory using the standard 6-311G* basis. By comparison to experimental normal mode frequencies deduced by Chapman [Spectrochim. Acta 24A(1968)1687] correction factors for predominant vibrational motions are determined and compared. Normal modes were decomposed into four nonredundant motions {As– As stretch, As– S stretch, As–S–As bend, and As–S–As wagging modes}.

We attempt to interpret the fluorescence of dipicolinic acid(2,6-pyridinedicarboxylic acid) and its ion by performing 6 in 6 complete active space MCSCF computations with the gaussian 92 program package using a 6-31G basis set. We report optimized geometries, charge densities, energies and vibrational frequencies for the ground state and first excited singlet state of dipicolinic acid and its ion. The theoretical results are used to predict and interpret the fluorescence of the acid and ion. It is argued that the results are relevant to the study of bacterial spores.