Ah inifio methods have been used to calculate the ground and excited states of "normal" and "hyper" porphyrins. Perturbation theory and C I methods were used to determine differential groundand excited-state correlation effects for [P"(P)F,]+ and [P"'(P)]+. A comparison is made to the INDO/S/CI predicted wavefunctions and spectra and to the experimental spectra of closely related molecules. The "hyper" [P"'(P)]+ calculations show some very low energy electronic transitions which provide an explanation for an anomalous "red" band in the spectrum and for the lack of fluorescence. Ah initio calculations also predict that (1) the lowest energy ' A , state is a two-configuration wavefunction which can be described as a diradical, (2) the two lowest-energy singlet excited states are double excitations from the closed shell SCF configuration, and (3) a 38, state is very close in energy to the lowest ' A , state.

Ab initio configuration interaction calculations are reported on the lowest quintet, triplet, and singlet states of Fe"(P). Due to the large number of states found, a catalog of the low-lying states is presented. Novel triplet and quintet charge-transfer states are reported as low as 1.3 eV. These states are d S (S = 5/2) on the iron low-spin-coupled to the radical anion excited porphyrin ring (S = 1/2 or 3/2). Oscillator strengths originating from each of three low-energy triplet states are reported.

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Single crystals of α-glycine with two, three, and five of the protons replaced by deuterium are studied at 4.2 K using electron–nuclear double resonance (ENDOR) spectroscopy to detect the NMR transitions of the distant deuterons on diamagnetic molecules. Complete deuteron quadrupole interaction tensors, and indirectly the electric field gradient tensors, are determined for all the labeled positions. Proton dipolar coupling tensors are also obtained for the methylene hydrogens in the case of glycine-d3. The relationship between the deuterium quadrupole coupling constants and the inverse cube of the bond length is refined and discussed. The resulting structural information including X–D bond lengths and bond angles is compared with data obtained by neutron diffraction. In addition, extensive calculations at both the semiempirical and ab initio levels are carried out to determine the electric field gradient at the hydrogen positions. Both intramolecular and lattice contributions are considered.