The observation of a picosecond transient in the relaxation of an iron porphyrin

Iron(III)tetraphenylporphyrin chloride, excited at 353 nm, showed significant bleaching and new absorption at 445 and 55 550 nm, which relaxed in 50 ps. Ground-state recovery occurs in ?100 fs; the bottleneck is populated with 3% efficiency. The photoproduct spectrum resembles a porphyrin ππ^* triplet, and provides evidence for intersystem crossing in an iron heme.     

On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.     

Partial photoionization cross sections of molecular oxygen

Measurements of partial photoionization cross sections of O₂ for excitation energies between 20 and 45 eV are reported and compared to a calculation using the Stieltjes-Tchebycheff moment theory. Positive evidence is obtained for a predicted σ-type shape resonance between 1 and 2 eV above threshold in certain ionic-state cross sections. Implications for angular distribution of photoelectrons from an oriented O₂ are discussed.     

The absorption spectrum of 4,4'-dimethyldiphenylmethylene dm 4,4'-dimethylbenzophenone crystals

A polarized absorption study of the low-lying excited triplet states of 4,4'-dimethyldiplicnylmethylene dispersed in single crystals of 4,4'-dimethylbenzophenone at 4.2 K is presented. Polarization measurements of the visible absorption spectrum, commencing at 4841.7 A. yield an electronic configuration of (pσ)¹ (π^*)¹ for the first cxcited triplet state. A second cxcited triplet state, (pπ)¹ (π^*)¹, lies ≈ 800 cm^?1 above this.     

Magnetic susceptibility of ruthenium(III) in tris-ethylenediamine salts. Effect of outer sphere ligands

The paramagnetic susceptibility of Ru(III) in tris-ethylenediamine salts has been measured as a function of temperature. In all cases the iodide salt exhibits a greater susceptibility than the bromide salt. This difference may be attributed to a larger degree of temperature independent paramagnetism in the iodide complex due to the presence of low lying charge transfer states.     

Interference effects in the predissociation of H2 and HD

Several absorption lines in the B? ¹Σ⁺_u ← X ¹Σ⁺_g system at 83 nm have been observed with sub-Doppler resolution in H₂ and HD. A detailed analysis of the lineshapes arising from the homogeneously predissociaied B ¹Σ⁺_u states shows that the linewidths are strongly affected by the Franck-Condon factors associated with coupling to the B' ¹Σ⁺_u continuum.     

Monte carlo simulation of three-body ion-ion recombination

The extent to which the use of models in discussing spectroscopic measurements of molecular reorientation in isotropic fluids is necessary, and possibly misleading, is discussed by considering the basic conditions imposed by molecular symmetry on reorientation.     

On the lattice of order ideals of an up-down poset

The combinatorial structure of the distributive lattice of order ideals of an up-down poset is studied. Two recursions are given for the Whitney numbers, and generating functions for the Whitney numbers are derived. In addition, an explicit nested chain decomposition is given for the lattice, the existence of which implies that the lattice satisfies the Sperner property and its generalizations, and has unimodal Whitney numbers.     

Extended fine structure analysis using electron beams

Appearance potential spectroscopy has found use primarily as a core level probe of the electronic structure of solid surfaces. The observation of extended fine structure above appearance potential edges, analogous to that observed above X-ray adsorption edges, gives promise that atomic spacings in the surface region may also be determined. Most previous studies of appearance potentials have depended on observing changes in the soft X-ray yield. Poor detection efficiencies and low flourescence yields have limited the usefulness of this approach. Using the secondary electron yield, however, we have recently succeeded in observing fine structure extending more than 400 eV above appearance potential edges. We are currently employing this approach to study the structure of SiO₂ films on Si substrates. Initial attempts at Fourier inversion and problems due to diffraction of the incident electron beam and multiple scattering effects will be discussed.