The 6Li,6Li-INADEQUATE Experiment: A New Tool for 1D- and 2D-NMR Studies of Organolithium Compounds

The 1D- and 2D-⁶Li, ⁶Li-INADEQUATE experiments are described as new tools for the detection of scalar coupled nonequivalent ⁶Li nuclei in organolithium clusters. Practical applications of these sequences are demonstrated for the ⁶Li-NMR spectra of (E)-1-lithio-2-(2-lithiophenyl)-1-phenylhex-1-ene ( 1 ) and (E)-2-lithio-1-(2-lithiophenyl)-1-phenylpent-1-ene ( 2 ), where signals due to dimers and monomers can be distinguished. The performance of the 2D-⁶Li, ⁶Li-INADEQUATE and the ⁶Li, ⁶Li-COSY-45-LR experiment are compared. The ⁶Li chemical shifts of 1 and 2 are discussed.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

Theoretical study of electronic structure of rhodium mononitride and interpretation of experimental spectra

Potential energy curves of 22 electronic states of RhN have been calculated by the complete active space second‐order perturbation theory method. The X¹Σ₀⁺ is assigned as the ground state, and the first excited state a³Π₀+ is 978 cm^?1 higher. The ¹Δ(I) and B¹Σ⁺ states are located at 9521 and 13,046 cm^?1 above the ground state, respectively. The B¹Σ⁺ state should be the excited state located 12,300 cm^?1 above the ground state in the experimental study. Moreover, two excited states, C¹Π and b³Σ⁺, are found 14,963 and 15,082 cm^?1 above the X¹Σ⁺ state, respectively. The transition C¹Π₁–X¹Σ₀⁺ may contribute to the experimentally observed bands headed at 15,071 cm^?1. There are two excited states, D¹Δ and E¹Σ⁺, situate at 20,715 and 23,145 cm^?1 above the X¹Σ⁺ state. The visible bands near 20,000 cm^?1 could be generated by the electronic transitions D¹Δ₂–a³Π₁ and E¹Σ⁺₀–X¹Σ⁺₀ because of the spin–orbit coupling effect. © 2013 Wiley Periodicals, Inc.     

Photoionization electronic spectroscopy of AlNa

Two electronic transitions are observed for a new heteronuclear dimer, AlNa, using two-color two-photon ionization spectrocopy (2R2PI). The combination of the analysis of vibronic structure and ab initio calculation enables us to assign the two transitions as D ¹Π←X ¹Σ⁺ and C ¹Σ⁺←X ¹Σ⁺; the origins of the D and C states are located at 16427 and 15422 cm⁻¹, and the vibrational frequencies being 151 cm⁻¹ in the D state, 115 cm⁻¹ in the C state, and 186 cm⁻¹ in the X state, respectively.     

Ab initio study of low-lying electronic states of the FNO2 molecule

Ab initio electronic structure calculations are reported for low-lying electronic states, ¹A₁, ¹A₂, ³A₂, ¹B₁, ³B₁, ¹B₂, and ³B₂ of the FNO₂ molecule. Geometric parameters for the ground state ¹A₁ are predicted by MRSDCI calculations with a double-zeta plus polarization basis set. The vertical excitation energies for these electronic states are determined using MRSDCI/DZ+P calculations at the ground-state equilibrium conformation. The oscillator strengths and radiative lifetimes for some electronic states are calculated based on the MRSDCI wave functions. © 1993 John Wiley & Sons, Inc.     

Experimental and theoretical studies of the valence-shell dipole excitation spectrum and absolute photoabsorption cross section of hydrogen fluoride

Absolute cross sectional measurements are reported of the valence-shell dipole excitation spectrum of HF obtained from suitably calibrated high impact energy, small momentum transfer, electron energy-loss scattering intensities. Detailed assignments are provided of all prominent features observed on the basis of concomitant single- and coupled-channel RPAE calculations. The measured spectrum, obtained at an energy resolution of = 0.06 eV (fwhm) in the = 9 to 21 eV interval, includes a dissociative feature centered at = 10.35 eV assigned as X¹Σ⁺ → (1π^?14σ)A¹Π, as well as numerous strong, sharp bands in the = 13 to 16 eV excitation energy region. These bands are attributed on basis of the present calculations to Rydberg (1π^?1npπ)-valence (3σ^?14σ) mixing in X¹Σ⁺ → ¹Σ⁺ excitation symmetry, which gives rise to a long conventional progression, and to strong 1π → nsσ, moderate 1π → ndσ, and weak 1π → npσ Rydberg series in X¹Σ⁺ → ¹Π excitation symmetry. A weaker 1π → ndπ Rydberg series also contributes to the spectrum in X¹Σ⁺ → ¹Σ⁺ symmetry. The calculated and measured excitation energies and f numbers, particularly for the X¹Σ → (1π^?14σ)A¹Π, → (1π^?13pπ)B¹Σ⁺, → (1π^?13sσ)C¹Π, and → (3σ^?14σ)D¹Σ⁺ transitions, are in good quantitative accord, suggesting that the overall nature of the HF spectrum is generally clarified on basis of the present studies. Finally, tentative assignments are provided of weak features observed above the 1π^?1 ionization threshold. As in previously reported joint experimental and theoretical studies of the valence-shell spectrum of F₂, high-resolution optical VUV measurements and calculated potential energy curves aid in the assignment and clarification of the HF spectrum.     

Some INDO calculations of the dependence of one-bond phosphorus-phosphorus coupling upon molecular geometry

Some INDO parameterized SCPT calculations of ¹J(P? P) and ¹J(P?P) are reported as a function of geometry. At structures corresponding to the gas-phase equilibrium configuration of diphosphine, all of the substituted diphosphines considered are predicted to have negative values of ¹J(P? P). Both contact and non-contact contributions to ¹J(P? P) are significant, whereas the angular variation of ¹J(P? P) is mainly due to the contact term. The non-contact interactions are dominant in determining the value of ¹J(P?P).     

Ab initio potential energy surfaces for BH+2

Preliminary ab initio calculations for the BH⁺₂ potential surface are presented. The reaction B⁺¹S) + H₂ → BH⁺ (B₂ (B²σ⁺) + H is shown to be most likely to occur for C_2v and near C_2v geometrics where there are avoided crossings between the 1 ¹A₁ and 2 ¹A₁ surfaces and between the 2 ¹A₁ and 3 ¹A₁ surfaces which should facilitate non-adiabatic transitions. Bent geometries are alos preferred for the reaction B⁺(¹S) + H₂ → BH⁺(A²π) + H for which there are avoided crossings in C₂ sysmmetry between surfaces correlating with 1 ¹A₁ and 1 ¹B₂ surfaces.     

Calculated coupling constants 1J(X–Y) and 1K(X–Y), and fundamental relationships among the reduced coupling constants for molecules HmX–YHn,with X,Y ═ 1H, 7Li, 9Be, 11B, 13C, 15N, 17O, 19F, 31P, 33S,and 35Cl

Equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) calculations have been performed to determine coupling constants ¹J(X–Y) for 65 molecules H_mX–YH_n, with X,Y ═ ¹H, ⁷Li, ⁹Be, ¹¹B, ¹³C, ¹⁵N, ¹⁷O, ¹⁹F, ³¹P, ³³S, and ³⁵Cl. The computed ¹J(X–Y) values are in good agreement with available experimental data. The reduced coupling constants ¹K(X–Y) have been derived from ¹J(X–Y) by removing the dependence on the magnetogyric ratios of X and Y. Patterns are found for the reduced coupling constants on a ¹K(X–Y) surface that are related to the positions of X and Y in the periodic table.     

Elektronisches Resonanz-Raman-Spektrum von Hexabromo-osmat(IV)

Electronic Resonance Raman Spectrum of Hexabromo Osmate(IV) Besides the vibrational bands there are other strong bands in the low-temperature Raman spectrum of [OsBr₆]^2?, which are independent from the excitation line and are interpreted as arising from transitions between the spin-orbit split components of the ³T_1g–Os⁴⁺ ground state. The band at 2800 cm^?1 is anomal polarized and attributable to Γ₁(³T_1g) → Γ₄(³T_1g), while the band at 4880 cm^?1 is depolarized and therefore assigned to Γ₁(³T_1g) → Γ₅(³T_1g). In the electronic Raman spectrum, too, a rigorous resonance-Raman effect is displayed and as far as six overtones of the stretching vibration A_1g and as many combination tones especially with T_2g are observed. Because of the dynamic Jahn-Teller effect Γ₁(³T_1g) → Γ₃(³T_1g) cannot be detected as an electronic Raman transition. Γ₁(³T_1g) → Γ₁(¹T_1g) at 15915 cm^?1 is obtained by luminescence absorption. The results are in good agreement with the absorption spectrum.     

Optically detected magnetic resonance study of the phosphorescent states of thiouracils

The triplet states of 1-methyl-2-thiouracil (1-Me-s²U), 1-methyl-4-thiouracil (1-Me-s²s⁴U) and 1-methyl-2,4-dithiouracil (1-Me-s² s⁴) have been investigated by optically detected magnetic resonance in zero magnetic field. The zero field splittings (ZFS) and the individual sublevel kinetic parameters are reported. The ZFS (|D|, |E|) values (in cm^?1) are found to increase in the order: 1-Me-s² U (0.2895, 0.0728) < 1-Me-s⁴U, (0.605, 0.0500) < 1-Me-s²s⁴ U (0.870, 0.0458). The triplet state lifetimes decrease in the same order, and both effects are attributed to an internal heavy atom effect of sulfur substitution. The vibronic structure of the phosphorescence emission indicates that the thiouracil phosphorescent states are ³(π, π^*). The low phosphorescence quantum yields of 1-Me-s⁴ U and of 1-Me-s²s⁴U result from radiationless decay of the triplet state rather than from inefficient intersystem crossing from the excited singlet state. The efficient radiationless decay of the triplet state appears to be a feature of the S-substitution at the 4-position of uracil. Phosphorescence polarization measurements of the individuals triplet sublevel emissions at ca. 1.2 K are consistent with 1-Me-s²U and 1-Me-s⁴U being non-planar in the phosphorescent state; the thiouracil phosphorescence from each triplet sublevel is polarized in the average plane of the distorted molecule. In the absence of σπ separability, spin—orbit mixing of ¹(π, π^*) and ³(π, π^*) states is enhanced and the radiative properties of the triplet state may be dominated by this mechanism rather than by the mixing of ¹(n, π^*), ¹(σ, π^*), or ¹(π, σ^*) with ³(π, π^* states which generally is the dominant mechanism for planar aromatic molecules.     

LCGTO MP LSD calculations for the diatomics PdX (X = C,Si, Ge,Sn)

Results are presented of a theoretical study of RhC, PdC, PdSi, PdGe and PdSn metal-alloy diatomics performed with the LCGTO MP LSD method. For the RhC molecule the computed electronic structure and spectroscpic constants are in good agreement with experimental data. The ground state of RhC is found to be ²Σ⁺ withe the lowest-lying excited state, ²II, at 10654 cm⁻¹ above the ground state, in good agreement with experiment and with ab initio CI calculations. For PdC and the other Pd-group IV A dimers the ground state is predicted to be ¹Σ and the two lowest-lying excited state are ³II (at 2718 cm⁻¹ for PdC) and ³gS (at 12164 cm⁻¹ for PdC). Our results are in disagreement with ab initio CI studies for PdC, which found a ³Σ ground state with a ³II lowest-lying excited state, and for PdGe, which found a ³II ground state followed by ³Σ⁻ and ¹Σ⁺.     

COMPLEX FORMATION BETWEEN PYRENE AND THE NUCLEOTIDES GMP, CMP, TMP AND AMP

Pyrene has been found to form ground and excited electronic state complexes of 1:1 stoichi-ometry with GMP, CMP, TMP and AMP. The values of their ground state association constants are 45 M^-1, 13M^-1, 14 M^-1, and 52 M^-1 respectively. The fluorescence of pyrene is strongly quenched by GMP, CMP, and TMP but only slightly by AMP. Fluorescence quenching analysis has yielded the values 87M^-1, 73 M^-1, and 154 M^-1 for the excited state association constants with GMP, CMP, and TMP, respectively. The corresponding values for the excited state second-order rate constant for complex formation are: 3.3 times 10⁹M^-1 s^-1 4.1 times 10⁹M^-1 s^-1, and 4.0 times 10⁹M^-1 s^-1. The probabilities of complex formation per collision between an excited pyrene molecule and a nucleotide are: 0.52, 0.64, and 0.63. The values for the excited state rate constant for dissociation of the complex are: 3.8 times 10⁷s^-1 5.6 times 10⁷s^-1, and 2.6 times 10⁷s^-1. The possibility is discussed that partial transfer of charge from pyrene to nucleotide may be playing a role in the complex formation process.     

Simulation of 2D H homo- and H-C heteronuclear NMR spectra of organic molecules by DFT calculations of spin-spin coupling constants and H and C-chemical shifts

Simulation of 2D ¹H homo- and ¹H-¹³C heteronuclear NMR spectra of organic molecules are here suggested as a tool in the structure elucidation of organic compounds. DFT calculations of ¹H and ¹³C chemical shifts are performed on a sample compound, the ethyl ester of the exo-2-norbornanecarbamic acid, with the mPW1PW91 method using the 6-31G(d) basis set, following a full optimization of the geometry. Homo and heteronuclear spin-spin coupling constants are also calculated, providing full prediction of the common 2D ¹H-¹H COSY, 2D ¹H-¹³C HSQC, and 2D ¹H-¹³C HMBC.     

Determination of trace elements in sea water by inductively-coupled plasma emission spectrometry

Pb, Zn, Cd, Ni, Mn, Fe, V and Cu in sea water are determined by extraction of their complexes with sodium diethyldithiocarbamate into chloroform, decomposition of the chelates and inductively-coupled plasma emission spectrometry. When 1-l water samples are used, the lowest determinable concentrations are: 0.063 μg Mn l^-1, 0.13 μg Zn l^-1, 0.25 μg Cd l^-1, 0.25 μg Fe l^-1, 0.38 μg V l^-1, 0.5 μg Ni l^-1, 0.5 μg Cu l^-1, and 2.5 μg Pb l^-1. Above these levels, the relative standard deviations are better than 12% for the complete procedure.     

Complete assignments of the 1H and 13C NMR spectra of 15 limonoids

Unambiguous and complete assignments of ¹H and ¹³C NMR chemical shifts for 15 limonoids, eight of them found in natural sources and seven other synthetic derivatives, are presented. The assignments are based on 2D shift‐correlated [¹H,¹H‐COSY, ¹H,¹³C‐gHSQC‐¹J(C,H), ¹H,¹³C‐gHMBC‐ⁿJ(C,H) (n = 2 and 3)] and NOE experiments. Copyright © 2003 John Wiley & Sons, Ltd.     

Multiphoton ionization spectra of two caged amines

The multiphoton ionization spectra of quinuclidine (ABCO) and triethylenediamine (DABCO) have been measured. All of the observed resonances are two-proton transitions to low-lying localized Rydberg states. For ABCO the lowest energy transitions are assigned as ¹A₁ (3s) ← ¹A₁ (n) 4.84 eV, and ¹E (3p_xy) ← ¹A₁ (n), 5.42 eV. In the case of DABCO, orbitals localized on the nitrogens interact and are split into two new orbitals. In terms of the split orbitals the low energy resonances in DABCO are assigned as ¹E′[3p_xy(?)] ← ¹A₁ (n+_, 4.44 eV, and ¹E″ [3p_xy(+)] ← ¹A₁ (n+), 4.94 eV.     

Magnetic double resonance studies of trimethyltin chalcogenides

NMR parameters for bis(trimethyltin) oxide, sulphide, selenide and telluride have been measured by ¹H{¹³C}, ¹H{⁷⁷Se}, ¹H{¹¹⁹Sn}, ¹H{¹²⁵Te}, and ¹H{¹¹⁷Sn} double resonance. Theories of ¹¹⁹Sn magnetic shielding and one-bond coupling constants are summarised and discussed in terms of the measured parameters. It is concluded that theoretical approximate expressions often used to estimate these parameters are inadequate when the tin atom is bound to selenium or tellurium.     

The kinetics of free radicals generated by IR laser photolysis. II. Reactions of C2(X 1Σ+g), C2(a 3Πu), C3(X̄ 1Σ+g) and CN(X 2Σ+) with O2

The 300 K reactions of O₂ with C₂(X ¹Σ⁺_g), C₂(a ³ Π_u), C₃(X? ¹Σ⁺_g) and CN(X ²Σ⁺), which are generated via IR multiple photon dissociation (MPD), are reported. From the spectrally resolved chemiluminescence produced via the IR MPD of C₂H₃CN in the presence of O₂, CO molecules in the a ³Σ⁺, d ³Δ_i, and e ³Σ^? states were identified, as well as CH(A ²Δ) and CN(B ²Σ⁺) radicals. Observation of time resolved chemiluminescence reveals that the electronically excited CO molecules are formed via the single-step reactions C₂(X ¹Σ⁺_g, a ³Π_u) + O₂ → CO(X ¹Σ⁺ + CO(T), where T denotes are electronically excited triplet state of CO. The rate coefficients for the removal of C₂(X ¹Σ⁺_g) and C₂(a ³Π_u) by O₂ were determined both from laser induced fluorescence of C₂(X ¹Σ⁺_g) and C₂(a ³Π_u), and from the time resolved chemiluminescence from excited CO molecules, and are both (3.0 ± 0.2)10^?12 cm³ molec^?1 s^?1. The rate coefficient of the reaction of C₃ with O₂, which was determined using the IR MPD of allene as the source of C₃ molecules, is <2 × 10^?14 cm³ molec^?1 s^?1. In addition, we find that rate coefficients for C₃ reactions with N₂, NO, CH₄, and C₃H₆ are all < × 10^?14 cm³ molec^?1 s^?1. Excited CH molecules are produced in a reaction which proceeds with a rate coefficient of (2.6 ± 0.2)10^?11 cm³ molec^?1 s^?1. Possible reactions which may be the source of these radicals are discussed. The reaction of CN with O₂ produces NCO in vibrationally excited states. Radiative lifetime of the ā ²Σ state of NCo and the ā ¹Π_u(000) state of C₃ are reported.     

A Field Effect Transistor Sensitive to the Phenobarbical Anion

Abstract

A field effect transistor sensitive to the phenobarbital anion is described. The response is Nernstian between 10^?1 mol 1^?1 and 10^?4 mol 1^?1 in the absence of added hydroxide, and 10^?1 mol 1^?1 to 10^?3 mol 1^?1 in the presence of added hydroxide. Selectivities over sulphate, chloride, nitrate, hydrogen phosphate have been determined and speed of response and stability are greater than the corresponding coated wire electrode.