Wave shapes in alternating DSC

ADSC with its periodical temperature programs combines the features of DSC measured at high heating rate (high sensitivity) with those at low heating rate (high temperature resolution). In addition, the “reversing” c_p effects can be separated from the “non-reversing” latent heat effects. Various periodical temperature programs can be applied. This paper compares the different possible temperature programs and their algorithms for the c_p determination for metal, metal oxide and polymer of various properties. Simulated and measured results for various wave shapes and samples are presented. The relevant sample properties and their influence on the measurements are identified and guiding rules for the proper choice of the various experimental parameters are given. Measurements with different samples, performed with the new METTLER TOLEDO STAR^e-System, are shown and compared with the simulation results. The simulations and the measurements clearly show that the alternating techniques can yield new information about sample properties, but are susceptible to the proper choice of the various experimental parameters.     

Multiple transient spectral holes in the R1-line of NaMgAl(oxalate)(3).9H2O:Cr(III). Probing excited and ground state g-factors in an external magnetic field of 15 mT

The gz-factors of the 4A2 ground state and the 2E excited state of chromium(III) doped into NaMgAl(oxalate)(3).9H2O are accurately determined at 2.5 K by the observation of multiple transient spectral holes in the R1-line (2E<--4A2 transition) in minute magnetic fields of approximately 15 mT.     

Conventional and Laser Photolysis of a Bisdiazo Compound

Entirely different product distributions were observed when the bisdiazo compound 1 was irradiated by a conventional lamp (254 nm) on the one hand and by a pulsed excimer laser (248 nm) on the other. Continuous photolysis gave a complex reaction mixture (Scheme 2), of which eight products were identified. Pulsed laser photolysis gave (11E)-dibenzocyclooctatriene 20 as a new product in 49% yield (Scheme 4). We postulate that compound 20 is formed via the biscarbene intermediate 18 which results from the sequential absorption of two photons by a single molecule within a single laser pulse.     

Side-hole to anti-hole conversion in time-resolved transient spectral hole-burning of emerald: ground state level versus excited state population storage in low magnetic fields

Time-resolved transient spectral hole-burning experiments in zero field and in low magnetic fields B( parallelc) are reported for the chromium(III) R(1)-line, 2A((2)E)<-- 2A((4)A(2)) of Chatham lab created emerald, Be(3)Al(2)Si(6)O(18)ratio Cr(III)(0.0017% per weight), in the temperature range of 3 to 12 K. In low magnetic fields and temperatures >5 K conversion of side-holes to anti-holes is observed with progressing time. Anti-holes are due to the population stored in ground state levels. The dynamics of the hole pattern can be well modelled by a set of coupled differential equations for the levels of the (4)A(2) and (2)E multiplets. The measurements allow the simultaneous determination of g-factors and spin-lattice relaxation rates in the excited state and the ground state. At 6 K the relaxation times between the split +/-1/2 2A((2)E) excited state levels and +/-3/2 2A((4)A(2)) levels of the ground state are about 0.16 ms and 9 ms, respectively. From the temperature dependence it follows that the spin-lattice relaxation rates are dominated by Orbach processes in the experimental temperature range.     

Metal complexes of macrocyclic ligands. Part XXIV. Binuclear complexes with tetraazamacrocycle-N,N′,N″,N‴-tetraacetic acids

The three ligands H₄dota, H₄teta, and H₄heta give binuclear complexes with Cu²⁺ and Ni²⁺, the spectral properties of which have been studied. The structures of Cu₂(dota)·5H₂O and Cu₂(teta)·6H₂O have been established by X-ray diffraction analysis.     

Spectral hole-burning and magnetic circular dichroism of matrix-isolated copper phthalocyanine

Persistent spectral hole-burning in the Q-band region is reported for a concentrated (≈ 2 × 10⁻² mol l⁻¹) matrix of copper phthalocyanine in solid Ar at 1.6 K. Hole-burning occurs with a quantum efficiency of ≈ 10⁻⁶ and can be reversed by annealing at ≈ 28 K. Vibrational side holes allow determination of excited-state frequencies. A hole-burning mechanism involving triplet-state charge separation followed by rapid electron back-transfer is proposed. Temperature dependence of the MCD and the difference between MCD spectra taken before and after irradiation indicate that the excited state is split by crystal-field and spin-orbit interactions.     

Metal Complexes with Macrocyclic Ligands. Part XLI. Nickel(II) and copper(II) complexes with mono-N-functionalized dithiadiazamacrocycles

Three N₂S₂ macrocycles ( 3, 10, 12 ) carrying an amino group as a pendant arm have been synthesized and their complexation properties towards Ni²⁺ and Cu²⁺ studied. The crystal structures of the Cu²⁺ complexes with 10-methyl-1,4-dithia-7,10-diazacyclododecane-7-ethanamine ( 3 ) and 11-methyl-1,4-dithia-8,11-diazacyclotetradecane-8-ethanamine ( 10 ) show that, in both cases, the Cu²⁺ is pentacoordinated by the four donor atoms of the macrocycle and the amino group of the side chain. In aqueous solution, however, two forms of the complexes with stoichiometries [MLH] and [ML] (M = Cu²⁺ or Ni²⁺) have been observed. In [MLH], the amino group is protonated and does not bind to the metal ion, whereas in [ML] the amino group is bound, and a pentacoordinated geometry results. The pK_a values for the equilibrium [ML] + H⁺?[MLH]⁺ decrease in the order 12 > 10 > 3 , indicating that the 2-aminoethyl side chain binds better to the Cu²⁺ than the 3-aminopropyl side chain. Cyclic voltammetry for the Cu²⁺/Cu⁺ pair shows that the 2-aminoethyl pendant arm stabilizes the Cu²⁺ oxidation state, when the metal ion is in the 14-membered ring ( 10 ), whereas it stabilizes Cu⁺ for the 12-membered macrocycle ( 3 ).     

Three‐dimensional ultra‐broadband integrated tapered mode multiplexers

The demonstration of a three‐dimensional tapered mode‐selective coupler in a photonic chip is reported. This waveguide‐based, ultra‐broadband mode multiplexer was fabricated using the femtosecond laser direct‐write technique in a boro‐aluminosilicate glass chip. A three‐core coupler has been shown to enable the multiplexing of the LP₀₁, LP and LP spatial modes of a multimode waveguide, across an extremely wide bandwidth exceeding 400 nm, with low loss, high mode extinction ratios and negligible mode crosstalk. Linear cascades of such devices on a single photonic chip have the potential to become a definitive technology in the realization of broadband mode‐division multiplexing for increasing optical fiber capacity.     

Exchange interactions in a trigonal chromium (III) dimer. Optical spectroscopy of tris-(μ-hydroxo)-bis-[(1,4,7-trimethyl-1, 4,7-triazacyclononane) chromium(III)] triperchlorate

High-resolution absorption, luminescence, Zeeman and MCD experiments were performed on single crystals of the title compound. The singlet-triplet and triplet-quintet exchange splittings in the ground state are 138 and 267 cm^?1, respectively. The corresponding exchange parameters are 2J= ?128 cm^?1 and j = 1.6 cm^?1. The zero-field splitting in the ground level is ?2.25 cm^?1. The lowest-energy emitting state is a ³E state, split into four spinor components with a total spread of 8 cm^?1.