Organic environments on Saturn’s moon,Titan: Simulating chemical reactions and analyzing products by FT-ICR and ion-trap mass spectrometry

Laboratory simulations have been carried out to model chemical reactions that possibly take place in the stratosphere of Saturn's moon, Titan. The aerosol products of these reactions (tholin samples) have been systematically analyzed by mass spectrometry using electrospray ionization (ESI) and laser desorption (LD). A wide variety of ions with a general formula C(x)H(y)N(z) detected by ultrahigh resolution and accurate mass measurements in a Fourier transform/ion cyclotron resonance (FT-ICR) cell reflect the complexity of these polymeric products, both in chemical compositions and isomeric distributions. As a common feature, however, tandem mass spectral (MS/MS) data and H/D exchange products in the solution phase support the presence of amino and nitrile functionalities in these (highly unsaturated) "tholin" compounds. The present work demonstrates that ESI-MS coupled with FT-ICR is a suitable and "intact" method to analyze tholin components formed under anaerobic conditions; only species with C(x)H(y)N(z) are detected for freshly prepared and harvested samples. However, when intentionally exposed to water, oxygen-containing compounds are unambiguously detected.     

Spectroscopic Study of Cm(III) Sorption onto gamma-Alumina

The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under an Ar atmosphere at an ionic strength of 0.1 M NaClO(4). The pH is varied between 2 and 10 and the metal ion concentration between 2.7x10(-8) and 4.5x10(-5) mol/L. With increasing pH, two Cm(III)-alumina surface species are identified which are attributed to identical withAl-O-Cm(2+)(H(2)O)(5) and identical withAl-O-Cm(+)(OH)(H(2)O)(4). The two curium-alumina surface complexes are characterized by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110&mgr;s). In the concentration range investigated, the surface complex formation is not dependent on the metal ion concentration but only on the pH. Additionally, the concentration ratio of the two surface species is found to be independent of the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages. Copyright 2001 Academic Press.     

Equilibrium and formation/dissociation kinetics of some Ln(III)PCTA complexes

The protonation constants () of 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA) and stability constants of complexes formed between this pyridine-containing macrocycle and several different metal ions have been determined in 1.0 M KCl at 25 degrees C and compared to previous literature values. The first protonation constant was found to be 0.5-0.6 log units higher than the value reported previously, and a total of five protonation steps were detected (log = 11.36, 7.35, 3.83, 2.12, and 1.29). The stability constants of complexes formed between PCTA and Mg2+, Ca2+, Cu2+, and Zn2+ were also somewhat higher than those previously reported, but this difference could be largely attributed to the higher first protonation constant of the ligand. Stability constants of complexes formed between PCTA and the Ln3+ series of ions and Y3+ were determined by using an "out-of-cell" potentiometric method. These values ranged from log K = 18.15 for Ce(PCTA) to log K = 20.63 for Yb(PCTA), increasing along the Ln series in proportion to decreasing Ln3+ cation size. The rates of complex formation for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA) were followed by conventional UV-vis spectroscopy in the pH range 3.5-4.4. First-order rate constants (saturation kinetics) obtained for different ligand-to-metal ion ratios were consistent with the rapid formation of a diprotonated intermediate, Ln(H(2)PCTA)(2+). The stabilities of the intermediates as determined from the kinetic data were 2.81, 3.12, 2.97, and 2.69 log K units for Ce(H(2)PCTA), Eu(H(2)PCTA), Y(H(2)PCTA), and Yb(H(2)PCTA), respectively. Rearrangement of these intermediates to the fully chelated complexes was the rate-determining step, and the rate constant (k(r)) for this process was found to be inversely proportional to the proton concentration. The formation rates (k(OH)) increased with a decrease in the lanthanide ion size [9.68 x 10(7), 1.74 x 10(8), 1.13 x 10(8), and 1.11 x 10(9) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively]. These data indicate that the Ln(PCTA) complexes exhibit the fastest formation rates among all lanthanide macrocyclic ligand complexes studied to date. The acid-catalyzed dissociation rates (k1) varied with the cation from 9.61 x 10(-4), 5.08 x 10(-4), 1.07 x 10(-3), and 2.80 x 10(-4) M(-1) s(-1) for Ce(PCTA), Eu(PCTA), Y(PCTA), and Yb(PCTA), respectively.     

Measuring hydrogen by cold-neutron prompt-gamma activation analysis

By irradiating with cold neutrons and avoiding hydrogenous materials of construction, we have developed a PGAA instrument at the Cold Neutron Research Facility at NIST with hydrogen detection limits in the microgram range in many materials. Quantities of 5–10 g H/g are presently measurable in gram-sized samples of silicon or quartz, and of order 0.01 wt % can be quantitatively measured in complex silicate rocks.Contributions of the National Institute of Standards and Technology are not subject to copyright.     

On the viability of small endohedral hydrocarbon cage complexes: X@C4H4, X@C8H8, X@C8H14, X@C10H16, X@C12H12, AND X@C16H16

Small hydrocarbon complexes (X@cage) incorporating cage-centered endohedral atoms and ions (X = H(+), H, He, Ne, Ar, Li(0,+), Be(0,+,2+), Na(0,+), Mg(0,+,2+)) have been studied at the B3LYP/6-31G(d) hybrid HF/DFT level of theory. No tetrahedrane (C(4)H(4), T(d)()) endohedral complexes are minima, not even with the very small hydrogen atom or beryllium dication. Cubane (C(8)H(8), O(h)()) and bicyclo[2.2.2]octane (C(8)H(14), D(3)(h)()) minima are limited to encapsulating species smaller than Ne and Na(+). Despite its intermediate size, adamantane (C(10)H(16), T(d)()) can enclose a wide variety of endohedral atoms and ions including H, He, Ne, Li(0,+), Be(0,+,2+), Na(0,+), and Mg(2+). In contrast, the truncated tetrahedrane (C(12)H(12), T(d)()) encapsulates fewer species, while the D(4)(d)() symmetric C(16)H(16) hydrocarbon cage (see Table of Contents graphic) encapsulates all but the larger Be, Mg, and Mg(+) species. The host cages have more compact geometries when metal atoms, rather than cations, are inside. This is due to electron donation from the endohedral metals into C-C bonding and C-H antibonding cage molecular orbitals. The relative stabilities of endohedral minima are evaluated by comparing their energies (E(endo)) to the sum of their isolated components (E(inc) = E(endo) - E(cage) - E(x)) and to their exohedral isomer energies (E(isom) = E(endo) - E(exo)). Although exohedral binding is preferred to endohedral encapsulation without exception (i.e., E(isom) is always exothermic), Be(2+)@C(10)H(16) (T(d)(); -235.5 kcal/mol), Li(+)@C(12)H(12) (T(d)(); 50.2 kcal/mol), Be(2+)@C(12)H(12) (T(d)(); -181.2 kcal/mol), Mg(2+)@C(12)H(12) (T(d)(); -45.0 kcal/mol), Li(+)@C(16)H(16) (D(4)(d)(); 13.3 kcal/mol), Be(+)@C(16)H(16) (C(4)(v)(); 31.8 kcal/mol), Be(2+)@C(16)H(16) (D(4)(d)(); -239.2 kcal/mol), and Mg(2+)@C(16)H(16) (D(4)(d)(); -37.7 kcal/mol) are relatively stable as compared to experimentally known He@C(20)H(20) (I(h)()), which has an E(inc) = 37.9 kcal/mol and E(isom) = -35.4 kcal/mol. Overall, endohedral cage complexes with low parent cage strain energies, large cage internal cavity volumes, and a small, highly charged guest species are the most viable synthetic targets.     

Chromatographic Determination of Silicon and Phosphorus as Molybdic Heteropoly Acids with Preconcentration

The chromatographic behavior of molybdic heteropoly acids of silicon and phosphorus as ion pairs with tetrabutylammonium bromide was studied by ion-pair high-performance liquid chromatography on the C₁₈reversed phase (UV detection at 310 nm). Heteropoly acids were preconcentrated as ion pairs with tetrabutylammonium bromide to increase the sensitivity of the determination. Optimal conditions were selected for the chromatographic determination of silicon and phosphorus in water in the presence of each other. Detection limits for silicon and phosphorus are (1.1 × 0.3) × 10^–3and (6.7 × 1.2) × 10^–3g/mL, respectively. Calibration plots are linear in the concentration ranges 0.01–0.1 g/mL (silicon) and 0.02–0.15 g/mL (phosphorus). The procedure was used for the analysis of distilled water.     

Optimal pressure conditions for unbiased external ion accumulation in a two-dimensional radio-frequency quadrupole for Fourier transform ion cyclotron resonance mass spectrometry.

When combined with on-line separations (e.g., capillary liquid chromatography (LC)), Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) provides a powerful tool for biological applications, and particularly proteomic studies. The sensitivity, dynamic range, and duty cycle provided by FTICR-MS have been shown to be increased by ion trapping and accumulation in a two-dimensional (2D) radio-frequency (rf)-only multipole positioned externally to an FTICR cell. However, it is important that ions be detected across the desired m/z range without a significant bias. In this work we found that pressure inside the accumulation rf-quadrupole plays an important role in obtaining "unbiased" ion accumulation. Pressure optimization was performed in both pulsed and continuous modes. It was found that unbiased accumulation in a 2D rf-only quadrupole could be achieved in the pressure range of 5 x 10(-4) to 5 x 10(-3) Torr. External ion accumulation performed at the optimal pressure resulted in an increase in both the spectrum acquisition rates and dynamic range.     

Kinetics and mechanism of acid-catalyzed oxidation of bromide ions by the aqueous chromyl(IV) ion

The reaction between the aqueous chromyl ion, CraqO2+, and Br- is acid-catalyzed and generates Br2. Kinetic studies that utilized a superoxochromium ion, CraqOO2+, as a kinetic probe yielded a mixed third-order rate law, -d[CraqO2+]/dt=k[CraqO2+][Br-][H+], where k=608+/-11 M-2 s-1. Experimental data strongly favor a one-electron mechanism, but the reaction is much faster than predicted on the basis of the reduction potential for the Br*/Br- couple. The reduction of CraqO2+ by transition-metal complexes, on the other hand, exhibits "normal" behavior, that is, k=(1.37x10(3)+1.94x10(3) [H+]) M-1 s-1 for Os(1,10-tris-phenanthroline)(3)2+ and <10 M-1 s-1 for Ru(2,2'-bipyridine)3(2+) at 0.1 M H+. The reduction of CraqOO2+ by Br2*- takes place with a rate constant k=(1.23+/-0.20)x10(9) M-1 s-1, as determined by laser-flash photolysis.     

Spectroscopic techniques and cyclic voltammetry with synthesis: manganese(II) coordination stability and its ligand field parameters effect on macrocyclic ligands

Manganese(II) macrocyclic complexes are prepared with different macrocyclic ligands, containing cyclic skeleton bearing organic components which have different chromospheres like N, O and S donor atoms and stereochemistry. Thus, six macrocyclic ligands, were prepared and their capacity to retain the manganese(II) ion in solid as well as in aqueous solution was determined and characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, mass, (1)H NMR, IR, electronic spectral and cyclic voltammetric studies. The electronic spectrum of this system showed a dependence that may be consistent with the formation of stable complexes and coordination behaviour of the ions. ESR spectra of all the complexes are recorded in solid as well as solution, which show the oxidation state of the manganese(II). Spin Hamiltonian manganese(II), which can be defined as the magnetic field vector (H): H = gBeta(e)HS + D[S(2)(z) - 35/12] + E[S(2)(z) - S(2)(y)] + ASI + (1/6)a [S(4)(x) + S(4)(y) + S(4)(z) - 707/16] + (1/180)F[(35S(2)(z) - 475)/(2S(2)(z) + 3255/10)] Significant distortion of the manganese(II) ion in observed geometry is evident from the angle subtended by the different membered chelate rings and the angles spanned by trans donor atoms octahedral geometry. Cyclic voltammetric studies indicate that complexes with all ligands undergoes one electron oxidation from manganese(II) to manganese(III) followed by a further oxidation to manganese(IV) at a significantly more positive potential.     

Infrared spectra of ThH2, ThH4, and the hydride bridging ThH4(H2)x (x = 1-4) complexes in solid neon and hydrogen

Laser-ablated Th atoms react with molecular hydrogen to give thorium hydrides and their dihydrogen complexes during condensation in excess neon and hydrogen for characterization by matrix infrared spectroscopy. The ThH2, ThH4, and ThH4(H2)x (x = 1-4) product molecules have been identified through isotopic substitution (HD, D2) and comparison to frequencies calculated by density functional theory and the coupled-cluster, singles, doubles (CCSD) method and those observed previously in solid argon. Theoretical calculations show that the Th-H bond in ThH4 is the most polarized of group 4 and uranium metal tetrahydrides, and as a result, a strong attractive "dihydrogen" interaction was found between the oppositely charged hydride and H2 ligands ThH4(H2)x. This bridge-bonded dihydrogen complex structure is different from that recently computed for tungsten and uranium hydride super dihydrogen complexes but is similar to that recently called the "dihydrogen bond" (Crabtree, R. H. Science 1998, 282, 2000). Natural electron configurations show small charge flow from the Th center to the dihydrogen ligands.     

Exploration of the potential energy surfaces, prediction of atmospheric concentrations, and prediction of vibrational spectra for the HO2...(H2O)n (n = 1-2) hydrogen bonded complexes

The hydroperoxy radical (HO2) plays a critical role in Earth's atmospheric chemistry as a component of many important reactions. The self-reaction of hydroperoxy radicals in the gas phase is strongly affected by the presence of water vapor. In this work, we explore the potential energy surfaces of hydroperoxy radicals hydrogen bonded to one or two water molecules, and predict atmospheric concentrations and vibrational spectra of these complexes. We predict that when the HO2 concentration is on the order of 10(8) molecules x cm(-3) at 298 K, that the number of HO2...H2O complexes is on the order of 10(7) molecules x cm(-3) and the number of HO2...(H2O)2 complexes is on the order of 10(6) molecules x cm(-3). Using the computed abundance of HO2...H2O, we predict that, at 298 K, the bimolecular rate constant for HO2...H2O + HO2 is about 10 times that for HO2 + HO2.     

Definition of magneto-structural correlations for the MnII ion

The electronic properties of the high spin mononuclear MnII complexes [Mn(tpa)(NCS)2] (1) (tpa=tris-2-picolylamine), [Mn(tBu3-terpy)2](PF6)2 (2) (tBu3-terpy=4,4',4'-tri-tert-butyl-2,2':6',2'-terpyridine) and [Mn(terpy)2](I)2 (3) (terpy=2,2':6',2'-terpyridine) with an N6 coordination sphere have been determined by multifrequency EPR spectroscopy. The X-ray structures of 1.CH3CN and 2.C4H10 O.0.5 C2H5OH.0.5 CH3OH reveal that the MnII ion lies at the center of a distorted octahedron. The D-values of 1-3 all fall in the narrow range of 0.041 to 0.105 cm(-1). The comparison of the results reported here and those found in the literature is consistent with the following observation: the D value is sensitive to the coordination number (6 or 5) of the MnII ion as long as the coordination sphere involves only nitrogen and/or oxygen based ligands. This magneto-structural correlation has been analyzed in this work though DFT model calculations. The zero-field splitting (zfs) parameters of 1-3 have been calculated and are in reasonable agreement with the experimental values. Hypothetical simplified models [Mn(NH3)x(OH2)y]2+ (x+y=5 or 6 and [Mn(NH3)5X]+ (X=OH, Cl)) have been constructed to investigate the origin of the zfs. This investigation reveals i) that D is sensitive to the coordination number (5 or 6) of the MnII ion, ii) for the five coordinate systems the major contribution to D is the spin-orbit coupling part, iii) for the six coordinate systems the major contribution to D is the spin-spin interaction and iv) the deprotonation of a water ligand leads to an increase of D, consistent with the relative ligand fields of OH(-) versus H2O.     

Kinetics of oxidation of nitroxyl radicals with superoxometal complexes of chromium and rhodium

In acidic aqueous solutions, nitroxyl radicals (X)TEMPO (X = H, 4-OH, and 4-oxo) and 3-carbamoyl-PROXYL readily reduce CraqOO2+ and Rh(NH3)4(H2O)OO2+ to the corresponding hydroperoxo complexes. The kinetics are largely acid independent for CraqOO2+, but acid catalysis dominates the reactions of the rhodium complex. This emerging trend in oxidations with superoxometal complexes seems to be directly related to the thermodynamics of electron transfer. The weaker the oxidant, the more important the acid-assisted path. The rate constants for the oxidation of (X)TEMPO by CraqOO2+ are 406 M(-1) s(-1) (X = H), 159 (4-OH), and (20. 6 + 77.5 [H+]) (4-oxo). For the rhodium complex, the values are (40 + 2.20 x 10(3) [H+]) (X = H), (25 + 1.10 x 10(3) [H+]) (4-HO), and 2.21 x 10(3) [H+] (4-oxo). An inverse solvent kinetic isotope effect, kH/kD = 0.8, was observed in the reaction between (O)TEMPO and (NH3)4(H(D))2O)RhOO2+ in 0.10 M H(D)ClO4 in H2O and D2O.     

Syntheses of cis- and trans-dibenzo-30-crown-10 derivatives via regioselective routes and their complexations with paraquat and diquat

cis-Dibenzo-30-crown-10 (cis-DB30C10) diester and trans-dibenzo-30-crown-10 (trans-DB30C10) diester were synthesized regioselectively with reasonable yields. These two isomers were further reduced to cis-dibenzo-30-crown-10 diol (1) and trans-DB30C10 diol (2), respectively. The complexations of cis- and trans-DB30C10 diols with paraquat (3) and diquat (4) were investigated by (1)H NMR, mass spectrometry, UV-vis spectroscopy, and single-crystal X-ray analysis. The reversible control of complexations of 1 x 3 and 2 x 3 by adding small molecules (KPF 6 and dibenzo-18-crown-6) was demonstrated by (1)H NMR. The addition of 2 molar equiv of KPF 6 is enough to dissociate 2 x 3 and 1 x 3 completely while the subsequent addition of 2 molar equiv of DB18C6 allows the two complexes to reform. However, 2 molar equiv of KPF6 cannot dissociate 1 x 4 and 2 x 4 completely. Because the DB30C10 cavity has a better geometry fit with paraquat 3 than with diquat 4, 4-based complexes have much higher association constants than the corresponding 3-based complexes. In the crystal structure of 1 x 4, the two hydroxymethyl groups of the crown ether 1 were joined by a "water bridge" to form a "supramolecular cryptand" while this kind of supramolecular cryptand structure was not observed in the crystal structure of 2 x 4. This is a possible reason for the increase in association constant from 2 x 4 (3.3 x 10(4) M(-1)) to 1 x 4 (5.0 x 10(4) M(-1)).     

Studies on the Synthesis of bis(Benzo diaza 23-crown-7) and its Complexes with K+, Mg2+, Ca2+ and Ba2+ Perchlorates

A novel (E,E)-dioxime (H2L) containing a 23-membered macrocyclic ionophore was synthesized from the reaction of 2,3-(4-aminobenzo)-1,4,11,14,17-pentaoxa-6,22-dioxo-7,21-diaza-cyclotricosane-2-ene (5) prepared from 2,3-(4-nitrobenzo)-1,4,11,14,17-pentaoxa-6,22-dioxo-7,21-diazacyclotricosane-2-ene (4) and cyanogen di-N-oxide (6). H2L encapsulates and coordinates to alkaline earth metal cations via the oxygen atom to form complexes, H2L2MX (M = K+, Mg2+, Ca2+ and Ba2+; X = ClO4-). After the complexation with alkaline earth metal cations, 1H-NMR, 13C-NMR and IR data were obtained and a comparison of these spectral data is presented.     

Micro gas analysis system for measurement of atmospheric hydrogen sulfide and sulfur dioxide

A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas collection. A thin porous membrane was pasted on a microchannel by the adhesive force of a fresh polydimethylsiloxane surface. The microchannel scrubber achieved much more efficient gas collection than conventional impingers and diffusion scrubbers. Two sets of the microchannel scrubbers and detectors were integrated in a 10 cm x 9 cm plastic board to create a micro gas analysis system (microGAS) for simultaneous measurements of H2S and SO2. The whole system including a battery was incorporated in a carrying case 34 cm W x 16 cm D x 17 cm H for use in the field. Liquid flows at 30 microl min(-1) were obtained by bimetal micropumps. The estimated detection limits were 0.1 ppbv for H2S and 1 ppbv for SO2. The system was demonstrated for real atmospheric gas analysis, and the results agreed well with data concurrently obtained by ion chromatography coupled with a cylindrical diffusion scrubber. The system we developed allowed automated continuous analyses in the field and achieved a much higher time resolution compared to those by ion chromatographic analysis.     

Visible and near-infrared intense luminescence from water-soluble lanthanide [Tb(III), Eu(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), Er(III)] complexes

The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a lanthanide (Ln) coordination site is reported [1 is 4-[(9-methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of water-soluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K(A) > or = 10(7) s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, phi(se), in air-equilibrated water were observed for the Ln.1 complexes of Eu(III) and Tb(III) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 x 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.     

Syntheses and Crystal Structures of Two New Main Group Metal Complexes （M = Al, Bi） with the Substituted p-Hydroquinones

The title complexes [Al(Hcah)(H2O)2]·2H2O (A) and [Bi(Hcah)(H2O)]n (B), where H4cah = 2-[N,N-bis(carboxymethyl)aminomethyl] hydroquinone, have been synthesized and characterized using X-ray single-crystal structure determination, IR and elemental analysis. Both complexes crystallize in the monoclinic system, space group P21/c with a = 7.8660(16), b = 10.096(2), c = 19.053(4) and β = 93.50(3)° for A; and those for B: a = 9.2348(18), b = 7.9061(16), c = 17.141(3) and β = 102.64(3)°. In addition, further investigation revealed that the central Al(III) ion in the mononuclear complex A is in a distorted octahedral coordination geometry, while structural analysis reveals that the Bi(III) ion is in a distorted pentagonal bipyramid, forming a 2-D polymeric complex B, and the coordination network is a 2D 4.82 net. The TG analyses of A indicate two steps of water loss.     

Synthesis and spectroscopic behavior of highly luminescent Eu(3+)-dibenzoylmethanate (DBM) complexes with sulfoxide ligands

In this paper the synthesis, characterization and photoluminescent behavior of the [RE(DBM)3L2] complexes (RE=Gd and Eu) with a variety of sulfoxide ligands; L=benzyl sulfoxide (DBSO), methyl sulfoxide (DMSO), phenyl sulfoxide (DPSO) and p-tolyl sulfoxide (PTSO) have been investigated in solid state. The emission spectra of the Eu(3+)-beta-diketonate complexes show characteristics narrow bands arising from the 5D0-->7F(J) (J=0-4) transitions, which are split according to the selection rule for C(n), C(nv) or C(s) site symmetries. The experimental Judd-Ofelt intensity parameters (Omega2 and Omega4), radiative (A(rad)) and non-radiative (A(nrad)) decay rates, and R02 for the europium complexes have been determined and compared. The highest value of Omega2 (61.9x10(-20)cm2) was obtained to the complex with PTSO ligand, indicating that Eu3+ ion is in the highly polarizable chemical environment. The higher values of the experimental quantum yield (q) and emission quantum efficiency of the emitter 5D0 level (eta) for the Eu-complexes with DMSO, DBSO and PTSO sulfoxides suggest that these complexes are promising Light Conversion Molecular Devices (LCMDs). The lower value of quantum yield (q=1%), for the hydrated complex [Eu(DBM)3H2O], indicates that the luminescence quenching occurs via multiphonon relaxation by coupling with the OH-oscillators from water molecule coordinated to rare earth ion. The pure red emission of the Eu-complexes has been confirmed by (x, y) color coordinates.     

Interaction of Hg Atom with Bare Si（111） Surface

1INTRODUCTION In the past decades,mercury has been a very use-ful electrode material in the fabrication and electrical measurement of molecule modified metal-metal and metal-semiconductor junctions.Majda et al.[1,2]constructed a symmetric Hg-SCn-CnS-Hg junction to study the electron tunneling properties of alkanethio-late bilayers.Whitesides et al.[3～5]fabricated Hg-SAM/SAM-Metal(Ag,Au,Cu)junctions to investi-gate the electrical breakdown voltage of self-assem-bled monolayers(SAMs…