A systematic study of the electronic structure and chemical binding in the dimer ion sequence, Ne2+, Ar2+, Kr+2, and Xe2+, has been carried out using density functional methods. For comparison, ab initio configuration-interaction calculations were also performed for the Ar2+ ion. These studies include detailed calculations of the pertinent potential energy curves and an analysis of the calculated spectroscopic properties of the bound states of these ions. A regular progression is found in the spectroscopic properties for the ground A 2Σ+1/2u state which leads to some remarkably simple conclusions concerning the nature of the binding and the size of these dimer ions. For the heavier systems, Kr2+ and Xe+2, spin–orbit coupling becomes important, resulting in a strong mixture of the Λ–S coupled Σ and Π states. This mixing affects the strength of the binding in the ground state. A comparison with other ab initio studies and an analysis of the asymptotic behavior at large internuclear separations is given. These dimer ion species illustrate the classic Hartree–Fock symmetry dilemma arising from improper dissociation character. The nature of this problem for ionized homopolar species is discussed.

cucumber cotyledons (9). We felt it was necessary to continue our studies on the nature of the metal to ascertain whether any ZnProto is synthesized under our experimental conditions. MATERIALS AND METHODS Reagents. EDTA (free acid), ATP (Na2 salt), GSH, and NAD were purchased from Sigma. Hepes, Tes, Cys, and BSA (fattyacid-poor) were obtained from Calbiochem. Diazald (N-methyl-N-nitroso-p-toluenesulfonamide) and 2-methylbutane were obtained from Aldrich Chemical Co. THF (stabilized analytical reagent) was obtained from Mallinckrodt. Proto was obtained from Porphyrin Products, Logan, UT; Mg-Proto-Me2 and ZnProto-Me2 were generous gifts of Dr. Kevin Smith, Department of Chemistry, University of California, Davis. Ammonium EDTA (NH4+EDTA) was prepared as foliows: 1 eq EDTA was stirred with 1.5 eq aqueous NH40H. The solution was brought to pH 7.7 with KOH and diluted to yield a 100 mm EDTA solution. Diazomethane was made by the decomposition of Diazald in concentrated alkali, was co-distilled with ether, and was collected in a receiver chilled to 0 C. Protoporphyrin IX Purification. Commercial available Proto was found to be of insufficient purity. Proto (Porphyrin Products) was, therefore, purified as follows. Approximately 10 mg Proto was suspended in 4 ml 95% ethanol containing 40 ,umol KOH and centrifuged briefly to clarify the suspension. The supernatant was decanted. This procedure was repeated 8 or 10 times until little or no more porphyrin dissolved. The supernatants were combined and the total volume was measured. To the alcoholic extract were added 0.33 volume H20 and 0.27 volume I M K-citrate (pH 4.0).The solution was brought back to pH with HCI. The alcoholic solution was extracted with I volume diethyl ether, and the lower phase was washed with 0.17 volume ether. The two ether extracts were combined, washed three times with equal volumes of H20, and stored at -15 C overnight. The ether was decanted without disturbing the ice crystals and was extracted with an equal volume of 10 mm KOH. The dissolved ether was removed by blowing N2 over the dilute KOH phase. A small aliquot of the latter was diluted into 25% w/w HCI and the Proto concentration was determined spectrophotometrically [A,. = 411 nm; EmM = 278 (2)]. Purified Proto was estimated to be 99% homogenous by HPLC, using a 405-nm absorbance detector.Preparation of Pheophytin. A hexane extract of Chl prepared from bean leaves (0.2 to 0.3 ml) was treated with an approximately equal volume of 6 M HCI. The mixture was shaken vigorously for 30 s in the dark. A large excess of H20 (30 ml) was added, and the mixture was extracted three times with 5 ml diethyl ether. The ether extract was washed several times with H20 to remove the HCI and was stored overnight at -15 C. The ether extract was decanted from the ice pellet and analyzed spectrofluorimetrically (Table I).Preparation of Methyl Pheophorbide. Peak I of the HPLC effluent (Fig. I)

Ultraviolet (254 nm) irradiation of liquid-cultured tobacco cells strongly and quickly inhibited their ability to incorporate labeled amino acids into protein. An incident dose of only 388 J/m2 reduced incorporation to 37 per cent of the original rate. The effect on amino acid incorporation did not seem to depend on inhibition of amino acid uptake, inhibition of the supply of nucleoside triphosphates, or inhibition of the supply of messenger RNA to cytoplasmic ribosomes.

Ultraviolet (254 -) radiation stimulated the efflux of MRb+ from liquidcultured tobacco (Nkotiana tabacum) cells; it did not stimulate the movement of mannitol or 2-deoxyglucose. These results indicate that the efflux of 'Rb+ is not to a generalized disruption of membrane structure.Previous studies have shown that UV radiation disrupts many plant cell functions, including photosynthesis, respiration, active transport, RNA and protein synthesis (10,15,16,21 (12,17,18) and that the K+ from the regular culture medium competed with the ssRb+ for uptake by the cells. The higher concentration of Ca2+ present in the incubation medium may also have promoted the absorption of ssRb+ (11,20). Fifty ml of cells were shaken in incubation medium for 24 hr, then placed in a beaker with sufficient MRb+ so that the cells would take up 0.08 to 0.27 nmol of ssRb+ (3.1-10.9 nCi)/ml of cells after 9 to 10 hr of labeling. The wide range of seRb+ taken up was probably due to differences in the densities of the cell suspensions. A typical cell suspension had a packed cell volume of about 0.04 ml/ml of suspension. To measure uptake, samples of cells were removed from the beaker, filtered on glass filter papers, and washed for about 15 sec with 30 ml of incubation medium which was supplemented with 20 mm KCI. The filtered cells were mixed with a dioxane-based scintillation fluid and counted in a liquid scintillation spectrometer (15). Cells were charged with 2-deoxy-D[l-3HJglucose (specific activity 21 Ci/mmol), and uptake was measured, essentially as described above, except that the cells were washed with unsupplemented incubation medium.Determination of MRb+ and 12-3HIDeoxyglucose Efflux. For the 86Rb+ studies, about 10 ml of labeled cells were filtered, washed for about 10 min with 200 ml of incubation medium supplemented with 20 mM KCI, and finally washed for about 5 min with 50 ml of incubation medium containing no K+ or Rb+. For the [2-3H] deoxyglucose experiment, 15 ml of labeled cells were washed for about 10 min with 75 ml of the unsupplemented incubation medium. In both experiments, the washed cells were transferred to 20 ml of incubation medium which was then subdivided into two 10-ml fractions, one for the control and the other for UV irradiation. At various times after irradiation, l-ml samples of cells plus medium were filtered and the filtrates were collected.One-quarter-ml aliquots of the filtrates were then mixed with the dioxane-based scintillation fluid for counting.

A technique for profiling of C over an atmospheric propagation path is proposed, developed and analyzed. The technique employs differential-tilt measurements to arrive at statistics which have unique weighting functions over the propagation path. These weighting functions are computed theoretically and used to derive a reconstructor matrix for C values throughout the path to be applied to an appropriate set of differential-tilt statistics. A candidate optical system is presented, and the performance of the profile reconstructor is analyzed. This study indicates that the relative error in the C estimates is approximately 5%. The relative error in estimating key atmospheric parameters such as the Fried parameter, isoplanatic angle, and the Rytov parameter from the reconstructed profiles is approximately 3%.