Internuclear distance and effects of Born-Oppenheimer breakdown for PtS, determined from its pure rotational spectrum

Platinum monosulfide PtS has been prepared in its X0(+) ground electronic state by laser ablation of Pt in the presence of H(2)S. The rotational spectra of eight isotopic species have been measured with a cavity pulsed jet Fourier-transform microwave spectrometer. Spectral analysis using a multi-isotopomer Dunham-type expression produced values for Y(01), Y(02), Y(11), and Y(21), along with large values for Born-Oppenheimer breakdown (BOB) parameters for both atoms of the molecule. The BOB parameters are rationalized in terms of the molecular electronic structure and nuclear field shift effects. A large negative (195)Pt nuclear spin-rotation constant has been rationalized in terms of the electron-nucleus dipole-dipole hyperfine constant. The equilibrium bond length in the Born-Oppenheimer approximation has been evaluated.     

Pure rotational spectra of PbSe and PbTe: potential function, Born-Oppenheimer breakdown, field shift effect and magnetic shielding

The pure rotational spectra of 41 isotopic species of PbSe and PbTe have been measured in their X 1Sigma+ electronic state with a resonator pulsed-jet Fourier transform microwave spectrometer. The molecules were prepared by laser ablation of suitable target rods and stabilised in supersonic jets of noble gas. Global multi-isotopologue analyses yielded spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as effective Born-Oppenheimer breakdown (BOB) coefficients delta01 for Pb, Se and Te. Unusual large values of the BOB parameters for Pb have been rationalized in terms of finite nuclear size (field shift) effect. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both PbSe and PbTe. Additionally, the magnetic hyperfine interactions produced by the uneven mass number A nuclei 207Pb, 77Se, 123Te, and 125Te were observed, yielding first determinations of the corresponding nuclear spin-rotation coupling constants.     

The rotational spectra, potential function, Born-Oppenheimer breakdown, and magnetic shielding of SnSe and SnTe

The pure rotational spectra of 27 isotopic species of SnSe and SnTe have been measured in the frequency range of 5-24 GHz using a Fabry-Perot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by laser ablation of suitable target rods and were stabilized in supersonic jets of Ar. Global multi-isotopolog analyses of all available high-resolution data produced spectroscopic Dunham parameters Y01, Y11, Y21, Y31, Y02, and Y12 for both species, as well as Born-Oppenheimer breakdown (BOB) coefficients delta01 for Sn, Se, and Te. A direct fit of the same data sets to an appropriate radial Hamiltonian yielded analytic potential energy functions and BOB radial functions for the X 1Sigma+ electronic state of both SnSe and SnTe. Additionally, the magnetic hyperfine interaction produced by the dipolar nuclei 119Sn, 117Sn, 77Se, and 125Te was observed, yielding first determinations of the corresponding spin-rotation coupling constants.     

Adsorption and dissociation of O2 on Pt-Co and Pt-Fe alloys

Self-consistent periodic density functional theory calculations (GGA-PW91) have been performed to study the adsorption of O and O(2) and the dissociation of O(2) on the (111) facets of ordered Pt(3)Co and Pt(3)Fe alloys and on monolayer Pt skins covering these two alloys. Results are compared with those obtained on two Pt(111) surfaces, one at the equilibrium lattice constant and the other laterally compressed by 2% to match the strain in the Pt alloys. The absolute magnitudes of the binding energies of O and O(2) follow the same order in the two alloy systems: Pt skin < compressed Pt(111) < Pt(111) < Pt(3)Co(111) or Pt(3)Fe(111). The reduced activity of the compressed Pt(111) and Pt skins for oxygen can be rationalized as being due to the shifting of the d-band center increasingly away from the Fermi level. We propose that an alleviation of poisoning by O and enhanced rates for reactions involving O may be some of the reasons why Pt skins are more active for the oxygen reduction reaction in low-temperature fuel cells. Finally, a linear correlation between the transition-state and final-state energies of O(2) dissociation on monometallic and bimetallic surfaces is revealed, pointing to a simple way to screen for improved cathode catalysts.     

The rotational spectra, potential function, Born-Oppenheimer breakdown, and hyperfine structure of GeSe and GeTe

The pure rotational spectra of 18 and 21 isotopic species of GeSe and GeTe have been measured in the frequency range 5-24 GHz using a Fabry-Pe?rot-type resonator pulsed-jet Fourier-transform microwave spectrometer. Gaseous samples of both chalcogenides were prepared by a combined dc discharge/laser ablation technique and stabilized in supersonic jets of Ne. Global multi-isotopologue analyses of the derived rotational data, together with literature high-resolution infrared data, produced very precise Dunham parameters, as well as rotational constant Born-Oppenheimer breakdown (BOB) coefficients (δ(01)) for Ge, Se, and Te. A direct fit of the same datasets to an appropriate radial Hamiltonian yielded analytic potential-energy functions and BOB radial functions for the X(1)Σ(+) electronic state of both GeSe and GeTe. Additionally, the electric quadrupole and magnetic hyperfine interactions produced by the nuclei (73)Ge, (77)Se, and (125)Te were observed, yielding much improved quadrupole coupling constants and first determinations of the spin-rotation parameters.     

Microwave spectra and structures of KrAuF, KrAgF, and KrAgBr; 83Kr nuclear quadrupole coupling and the nature of noble gas-noble metal halide bonding

Microwave spectra of the complexes KrAuF and KrAgBr have been measured for the first time using a cavity pulsed jet Fourier transform microwave spectrometer. The samples were prepared by laser ablation of the metal from its solid and allowing the resulting plasma to react with an appropriate precursor (Kr, plus SF6 or Br2) contained in the backing gas of the jet (usually Ar). Rotational constants; geometries; centrifugal distortion constants; vibration frequencies; and 197Au, 79Br, and 81Br nuclear quadrupole coupling constants have all been evaluated. The complexes are unusually rigid and have short Kr-Au and Kr-Ag bonds. The 197Au nuclear quadrupole coupling constant differs radically from its value in an AuF monomer. In addition 83Kr hyperfine structure has been measured for KrAuF and the previously reported complex KrAgF. The geometry of the latter has been reevaluated. Large values for the 83Kr nuclear quadrupole coupling constants have been found for both complexes. Both the 197Au and 83Kr hyperfine constants indicate a large reorganization of the electron distribution on complex formation. A thorough assessment of the nature of the noble gas-noble metal bonding in these and related complexes (NgMX; Ng is a noble gas, M is a noble metal, and X is a halogen) has been carried out. The bond lengths are compared with sums of standard atomic and ionic radii. Ab initio calculations have produced dissociation energies along with Mulliken populations and other data on the electron distributions in the complexes. The origins of the rigidity, dissociation energies, and nuclear quadrupole coupling constants are considered. It is concluded that there is strong evidence for weak noble gas-noble metal chemical bonding in the complexes.     

Infrared spectra of seeded hydrogen clusters: (paraH2)N - OCS, (orthoH2)N - OCS, and (HD)N - OCS, N = 2 - 7

Infrared spectra of hydrogen-carbonyl sulfide clusters containing paraH2, orthoH2, or HD have been studied in the 2060 cm(-1) region of the C-O stretching vibration. The clusters were formed in pulsed supersonic jet expansions and probed using a tunable infrared diode laser spectrometer. Simple symmetric rotor type spectra were observed and assigned for clusters containing up to N = 7 hydrogen molecules. There was no resolved K structure, and Q-branch features were present for orthoH2 and HD but absent for paraH2. These characteristics can be rationalized in terms of near symmetric rotor structures, very low effective rotational temperatures (0.15 to 0.6 K), and nuclear spin statistics. The observed vibrational shifts were compared with those from recent observations on the same clusters embedded in helium nanodroplets. The observed rotational constants for the paraH2 clusters are in good agreement with a recent quantum Monte Carlo simulation. Some mixed clusters were also observed, such as HD-HD-He-OCS and paraH2 - orthoH2 - OCS.     

Rotational spectra of the Xe-(H2O)2 van der Waals trimer: xenon as a probe of electronic structure and dynamics

Rotational spectra of three isotopomers of the Xe-(H2O)2 van der Waals trimer were recorded using a pulsed-nozzle, Fourier transform microwave spectrometer. Nine [nine, four] a-type and twelve [eleven, seven] b-type transitions were measured for the 132Xe-(H2O)2 [129Xe-(H2O)2, 131Xe-(H2O)2] isotopomer. The determined rotational and centrifugal distortion constants were used to extract information about the structure and vibrational motions of the complex. The nuclear quadrupole hyperfine structures due to the 131Xe (nuclear spin quantum number I=3/2) nucleus were also detected. The large value of the off-diagonal nuclear quadrupole coupling constant chiab in particular provides detailed insight into the electronic environment of the xenon atom and the orientations of the water molecules within the complex. An effective structure that best reproduces the experimental 131Xe nuclear quadrupole coupling constants is rationalized by ab initio calculations. An overall goal of this line of work is to determine how the successive solvation of a xenon atom with water molecules affects the xenon electron distribution and its intermolecular interactions. The results may provide molecular level interpretations of 129Xe NMR data from, for example, imaging experiments.     

Theoretical investigation of the apparently irregular behavior of pt-pt nuclear spin-spin coupling constants

One-bond Pt-Pt nuclear spin-spin coupling constants J(Pt-Pt) for closely related dinuclear Pt complexes can differ by an order of magnitude without any obvious correlation with Pt-Pt distances. As representative examples, the spin-spin couplings of the dinuclear Pt(I) complexes [Pt(2)(CO)(6)](2+) (1) and [Pt(2)(CO)(2)Cl(4)](2-) (2) have been computationally studied with a recently developed relativistic density functional method. The experimental values are (1)J((195)Pt-(195)Pt) = 5250 Hz for 2 but 551 Hz for 1. Many other examples are known in the literature. The experimental trends are well reproduced by the computations and can be explained based on the nature of the ligands that are coordinated to the Pt-Pt fragment. The difference for J(Pt-Pt) of an order of magnitude is caused by a sensitive interplay between the influence of different ligands on the Pt-Pt bond, and relativistic effects on metal-metal and metal-ligand bonds as well as on "atomic orbital contributions" to the nuclear spin-spin coupling constants. The results can be intuitively rationalized with the help of a simple qualitative molecular orbital diagram.     

Rotational spectra, structures, hyperfine constants, and the nature of the bonding of KrCuF and KrCuCl

Rotational spectra of KrCuF and KrCuCl have been measured in the frequency range 8-18 GHz, using a pulsed jet cavity Fourier transform microwave spectrometer. The molecules were prepared by ablating Cu metal with a pulsed Nd:YAG laser (1064 nm) and allowing the plasma to react with appropriate precursors (Kr plus SF(6) or Cl(2)) contained in the backing gas of the jet (Ar or Kr). Rotational constants, internuclear distances, vibration frequencies, and (83)Kr, Cu, and Cl nuclear quadrupole coupling constants have all been evaluated. The Kr-Cu bonds are short and the complexes are rigid. The (83)Kr coupling constant of KrCuF is large (128.8 MHz). The Cu nuclear quadrupole coupling constants differ radically from those of uncomplexed CuF and CuCl molecules. The results are supported by those of ab initio calculations, which have also yielded Mulliken populations, MOLDEN plots of valence molecular orbitals and Laplace concentrations, and electron localization functions. The results are consistent with those reported earlier for other noble gas-noble metal halide complexes. The results have been used to assess the nature of the bonding in the complexes and have produced good evidence for weak noble gas-noble metal chemical bonding.     

Pitzer理论在含有机物的HCl-H2SO4-葡萄糖多组分电解质水溶液中的应用

在298.15K,以葡萄糖质量分数(0.15)恒定的葡萄糖+水混合物为溶剂,测定了电池Pt,H2(101.325kPa)|HCl(m1),H2SO4(m2),Glucose(x),H2O(1-x)|AgCl-Ag的电动势.用所得数据确定了H2SO4在该混合溶剂中的二级解离常数(K2)和一级介质效应.用带有中性分子与各离子相互作用项的Pitzer方程表示Owen定义的总介质效应可较好地处理含有机物的多组分电解质水溶液体系,并用此法处理了文献中HCl在各混合溶剂中的活度系数实验数据,确定了HCl与有机物分子相互作用的Pitzer参数.     

The (CH2)2O-H2O hydrogen bonded complex. Ab Initio calculations and Fourier transform infrared spectroscopy from neon matrix and a new supersonic jet experiment coupled to the infrared AILES beamline of synchrotron SOLEIL

A series of hydrogen bonded complexes involving oxirane and water molecules have been studied. In this paper we report on the vibrational study of the oxirane-water complex (CH(2))(2)O-H(2)O. Neon matrix experiments and ab initio anharmonic vibrational calculations have been performed, providing a consistent set of vibrational frequencies and anharmonic coupling constants. The implementation of a new large flow supersonic jet coupled to the Bruker IFS 125 HR spectrometer at the infrared AILES beamline of the French synchrotron SOLEIL (Jet-AILES) enabled us to record first jet-cooled Fourier transform infrared spectra of oxirane-water complexes at different resolutions down to 0.2 cm(-1). Rovibrational parameters and a lower bound of the predissociation lifetime of 25 ps for the v(OH)(b) = 1 state have been derived from the rovibrational analysis of the ν(OH)(b) band contour recorded at respective rotational temperatures of 12 K (Jet-AILES) and 35 K (LADIR jet).     

Nuclear quadrupole hyperfine structure in the microwave spectrum of HCl-N2O: electric field gradient perturbation of N2O by HCl

The microwave spectra of six isotopomers of HCl-N(2)O have been obtained in the 7-19 GHz region with a pulsed molecular beam, Fourier transform microwave spectrometer. The nuclear quadrupole hyperfine structure due to all quadrupolar nuclei is resolved and the spectra are analyzed using the Watson S-reduced Hamiltonian with the inclusion of nuclear quadrupole coupling interactions. The spectroscopic constants determined include rotational constants, quartic and sextic centrifugal distortion constants, and nuclear quadrupole coupling constants for each quadrupolar nucleus. Due to correlations of the structural parameters, the effective structure of the complex cannot be obtained by fitting to the spectroscopic constants of the six isotopomers. Instead, the parameters for each isotopomer are calculated from the A and C rotational constants and the chlorine nuclear quadrupole coupling constant along the a-axis, chi(aa). There are two possible structures; the one in which hydrogen of HCl interacts with the more electronegative oxygen of N(2)O is taken to represent the complex. The two subunits are approximately slipped parallel. For H (35)Cl-(14)N(2)O, the distance between the central nitrogen and chlorine is 3.5153 A and the N(2)O and HCl subunits form angles of 72.30 degrees and 119.44 degrees with this N-Cl axis, respectively. The chlorine and oxygen atoms occupy the opposite, obtuse vertices of the quadrilateral formed by O, central N, Cl, and H. Nuclear quadrupole coupling constants show that while the electric field gradient of the HCl subunit remains essentially unchanged upon complexation, there is electronic rearrangement about the two nitrogen nuclei in N(2)O.     

Tuning the emissive triplet excited states of platinum(II) Schiff base complexes with pyrene, and application for luminescent oxygen sensing and triplet-triplet-annihilation based upconversions

Pt(II) Schiff base complexes containing pyrene subunits were prepared using the chemistry-on-complex approach. This is the first time that supramolecular photochemical approach has been used to tune the photophysical properties of Schiff base Pt(II) complexes, such as emission wavelength and lifetimes. The complexes show intense absorption in the visible region (ε = 13100 M(-1) cm(-1) at 534 nm) and red phosphorescence at room temperature. Notably, much longer triplet excited state lifetimes (τ = 21.0 μs) were observed, compared to the model complexes (τ = 4.4 μs). The extension of triplet excited state lifetimes is attributed to the establishment of equilibrium between the metal-to-ligand charge-transfer ((3)MLCT) state (coordination centre localized) and the intraligand ((3)IL) state (pyrene localized), or population of the long-lived (3)IL triplet excited state. These assignments were fully rationalized by nanosecond time-resolved difference absorption spectra, 77 K emission spectra and density functional theory calculations. The complexes were used as triplet sensitizers for triplet-triplet-energy-tranfer (TTET) processes, i.e. luminescent O(2) sensing and triplet-triplet annihilation (TTA) based upconversion. The O(2) sensitivity (Stern-Volmer quenching constant) of the complexes was quantitatively evaluated in polymer films. The results show that the O(2) sensing sensitivity of the pyrene containing complex (K(SV) = 0.04623 Torr(-1)) is 15-fold of the model complex (K(SV) = 0.00313 Torr(-1)). Furthermore, significant TTA upconversion (upconversion quantum yield Φ(UC) = 17.7% and the anti-Stokes shift is 0.77 eV) was observed with pyrene containing complexes being used as triplet sensitizers. Our approach to tune the triplet excited states of Pt(II) Schiff base complexes will be useful for the design of phosphorescent transition metal complexes and their applications in light-harvesting, photovoltaics, luminescent O(2) sensing and upconversion, etc.     

Weak, improper, C-O...H-C hydrogen bonds in the dimethyl ether dimer

The ground-state rotational spectrum of the dimethyl ether dimer, (DME)(2), has been studied by molecular beam Fourier transform microwave and free jet millimeter wave absorption spectroscopies. The molecular beam Fourier transform microwave spectra of the (DME-d(6))(2), (DME-(13)C)(2), (DME-d(6))...(DME), (DME-(13)C)...(DME), and (DME)...(DME-(13)C) isotopomers have also been assigned. The rotational parameters have been interpreted in terms of a C(s) geometry with the two monomers bound by three weak C-H...O hydrogen bonds, each with an average interaction energy of about 1.9 kJ/mol. The experimental data combined with high-level ab initio calculations show this kind of interaction to be improper, blue-shifted hydrogen bonding, with an average shortening of the C-H bonds involved in the hydrogen bonding of 0.0014 A. The length of the C-H...O hydrogen bonds, r(O...H), is in the range 2.52-2.59 A.     

Vibrational spectra and structure of gaseous and solid dimethylboric anhydride

The Raman spectra of gaseous, liquid and solid dimethylboric anhydride (CH₃)₂BOB(CH₃)₂ have been recorded from 10–3500 cm^?1. The IR spectra from 4000–30 cm^?1 have also been recorded. The spectra of the gaseous phase have been interpreted in terms of C₂ symmetry implying a bent B-O-B skeleton with the B(CH₃)₂ groups twisted and consistent with a rather larger barrier to internal rotation about the B-O bonds. The spectra of the crystalline state, however, suggest that the molecular symmetry is altered upon solidification. Isotopic substitution of the oxygen atom by ¹⁸O confirmed that the B-O-B skeleton is linear in the solid state, and the spectra have been interpreted in terms of D_2h molecular symmetry.     

Photochemistry of a crown ether styryl dye adsorbed on silica gel and in acetonitrile solution: a comparative flash photolysis study

The photochemical behaviour of a photochromic crown ether styryl dye (BOB) adsorbed on silica gel has been found by a steady-state technique to be similar to that observed in a fluid solution of high polarity. The intermediate spectra obtained by diffuse reflectance laser flash photolysis of BOB on silica gel in a nitrogen atmosphere have been preliminarily attributed to the triplet-triplet (T-T) absorption of BOB and the absorption of BOB cation radicals. For comparison, the absorption spectrum of BOB triplets with a lifetime of ∼0.8 μs in acetonitrile solution has been obtained using biphenyl as a sensitizer.     

Particle-size effect of nanoscale platinum catalysts in oxygen reduction reaction: an electrochemical and 195Pt EC-NMR study

Oxygen reduction reaction (ORR) measurements and (195)Pt electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy were combined to study a series of carbon-supported platinum nanoparticle electrocatalysts (Pt/CB) with average diameters in the range of roughly 1-5 nm. ORR rate constants and H(2)O(2) yields evaluated from hydrodynamic voltammograms did not show any particle size dependency. The apparent activation energy of 37 kJ mol(-1), obtained for the ORR rate constant, was identical to that obtained for bulk platinum electrodes. Pt/CB catalysts on Nafion produced only 0.7-1% of H(2)O(2), confirming that the direct four-electron reduction of O(2) to H(2)O is the predominant reaction. NMR spectral features showed characteristic size dependence, and the line shapes were reproduced by using the layer-deconvolution model. Namely, the variations in the NMR spectra with particle size can be explained as due to the combined effect of the layer-by-layer variation of the s-type and d-type local density of states. However, the surface peak position of (195)Pt NMR spectra and the spin-lattice relaxation time of surface platinum atoms showed practically no change with the particle size variation. We conclude that there is a negligible difference in the surface electronic properties of these Pt/CB catalysts due to size variations and therefore, the ORR activities are not affected by the differences in the particle size.     

Electron paramagnetic resonance spectrum of the FCO2 radical isolated in noble gas matrices

The EPR spectra of the fluoroformyloxyl radical FCO(2) isolated in noble gas matrices at temperatures from 5 to 30 K have been investigated. This study provides principal g values and (19)F hyperfine coupling constants of FCO(2) measured in Ar matrices at 5 K, and yields isotropic values at 30 K. A detailed analysis of the coupling parameters obtained from the EPR and a concomitant high resolution spectroscopic MMW study supported by quantum chemical calculations rationalized the fine and hyperfine interactions of this simple fluorooxyl radical.     

Analysis of the hyperfine structures and Λ doubling of high-resolution LMR spectra of 15N16O (X2Ⅱ)

From the theories of the nuclear hyperfine structure (HFS) and Λ doubling of diatomic molecules, several brief algebraic equations for interpretation of HFS and Λ doubling of transitions of diatomic molecule have been developed. A few important parameters of HFS and Λ doubling of 15N16O have been efficiently and accurately obtained from the analysis of the high resolution spectra of 15N16O (X2Ⅱ) observed in our experiments with these equations. This method can provide an effective approach to obtain important hyperfine parameters of novel radicals from their high resolution laser magnetic resonance spectra.