Diazabutadienes as ligands: I. Compounds of aluminium: coordination of diazabutadienes to Al(CH3)3 and subsequent intramolecular insertion and rearrangement reactions leading to (CH3)2AIR—N—CH(CH3)—C(R')=N—R(R'= H,CH3) and (CH3)2AIR—N—CH2—C(CH3)=N—R

Reaction of R—N=CH—CH=N—R with [(CH₃)₃Al]₂ affords the coordination product (CH₃)₃AlRN=CH—CH=NR (A) for R = 2,6-(CH₃)₂C₆H₃ and 2,4,6(CH₃)₃C₆H₂. For R = 4 ClC₆H₄, 4-CH₃C₆H₄ and 4-CH₃OC₆H₄, insertion takes place, giving the complexes (CH₃)₂A$\text{lRN—CH(CH}{}_3\text{)—CH=N}$—R (B), in which Al is part of a five-membered chelate ring. Depending on the temperature both the addition and insertion products rearrange intramolecularly to the complexes (CH₃)₂-A$\text{lR—N—CH}{}_2\text{—C(CH}{}_3\text{)=N}$—R (C), in which Al is also part of a five-membered chelate ring. Reactions of the asymmetric (CH₃)₂HC—N=CH—C(CH₃)=N—CH-(CH₃)₂ with [Al(CH₃)₃]₂ also leads to an insertion product, (CH₃)₂A$\text{lRN-—CH(CH}{}_3\text{)—C(CH}{}_3\text{)=N}$—R (B') (R = (CH₃)₂CH), but there is no subsequent rearrangement in this case.A mechanism involving hydrogen migration is tentatively proposed to account for the observed isomerization, which increases in rate in the order:R = (CH₃)₃C>2,4,6-(CH₃)₃C₆H₂> 2,6-(CH₃)2C₆H₃ (A → C)andR = 4-CH₃OC₆H₄>4-CH₃C₆H₄>4-ClC₆H₄ (B → C)Hydrolysis of isomer C gives the unknown imino amines R—NH—CH₂-C(CH₃)=N—R in quantitative yield.     

Second excited singlet state emission spectroscopy of thiocarbonyls. II. Thiocarbonyl chlorofluoride

Single vibronic level emission spectra have been measured for four excitation wavelengths pumping the second excited singlet state of CIFCS. Only resonance fluorescence is observed. Progressions involving Δv″₁ = 0, 1, 2, …, Δv″₆ = 0, 2, 4 … dominate. Analysis of the spectra indicates that neither intra- or intermolecular processes lead to odd Δv′₆ changes and that collisions in the pure gas lead to electronic quenching of molecules in the excited state.     

Second excited singlet state emission spectroscopy of thiocarbonyls. I. Thiophosgene

Well resolved emission spectra have been recorded after dye laser excitation of low-lying vibronic levels in the $\text{B}$(¹A₁) state of Cl₂CS. The effects of substrate pressure, added SF₆ and excitation wavelength on the spectra are reported. A Franck-Condon analysis suggests that the excited state CS bond length is 0.5 Å longer than in the ground state.     

Temperature dependence of fluorescence and phosphorescence from probe molecules in polymer substrates

The effect of temperature on the fluorescence and phosphorescence from a series of indole and coumaric acid derivatives incorporated in poly(methyl methacrylate), poly(styrene) and poly(vinyl alcohol) substrates has been investigated in the range 90–300 K. Activation energies for the temperature-dependent non-radiative decay of the triplet excited states showed abrupt changes at temperatures corresponding to the onset of local relaxation processes in the polymers. The values of activation energies and transition temperatures in any one polymer did not depend greatly on the probe, suggesting that the temperature-dependent triplet state deactivation mechanisms are mainly influenced by extrinsic polymer properties. However, the effect of temperature on the fluorescence intensity was found to depend markedly on the probe and state of ionization of any one probe. Possible explanations for these observations are presented.     

The unexpected formation of a lithium-enolate from bis2-[(dimethylamino)methyl]phenyl copper lithium. X-ray structure of Li4[OC(CH2)C6H4CH2NMe2-2]4

Attempted crystallization of the bis(aryl)lithium cuprate, Cu₂Li₂(C₆H₄CH₂-NMe₂-2)₄, from diethyl ether/pentane afforded in according to an X-ray diffraction analysis appeared to be the lithium enolate, Li₄[OC(=CH₂)C₆H₄CH₂NMe₂-2]₄. This consists of a central Li₄O₄ cube with intramolecular LiN coordination of the CH₂NMe₂ substituent. This enolate, which has also been prepared via an independent route, is the first example of a structurally characterized lithium enolate and contains Li centres that are intramolecularly coordinated.     

A high pressure thermobalance

A high pressure thermobalance was assembled by placing a DuPont Model 950 balance into a stainless steel enclosure. The thermobalance is capable of operation to a maximum pressure (of N₂) to 500 atm and to a maximum temperature of 500°C. Operation of the instrument is illustrated by the thermogravimetric curves of BaBr₂·2H₂O, CuSO₄·5H₂0 and NaHCO₃ at various pres     

Intermode energy transfer in vibrationally excited O3

The laser excited fluorescence method has been employed to determine the rate constants for vibrational relaxation of the O₃ (010), O₃ (100) and O₃ (001) levels at 298 K. The fluorescence observations from the O₃ (010) level provide direct measurements of the rate for intermode vibrational energy transfer from the coupled ν₁ and ν₃ modes to the ν₂ mode. The slowness of this process indicates the likelihood that the ν₁ and/or ν₃ modes (rather than the ν₂ mode) play a predominant role in the laser enhanced reaction between O₃² and NO at 298 K.     

Laser induced predissociation of SF6 clusters

Dimer predissociation is sensitively detected as attenuation of the SF⁺₅ ion signal from a SF₆ molecular beam crossed by a line tunable cw CO₂ laser. The dimer spectra show a double peak structure which is assigned to the symmetric and anti-symmetric combination of the v₃ vibration. The minimum observed linewidth is 3 cm^?1 fwhm.     

Laser flash spectroscopy of iodine and iodoform

The absorption spectra and decay times of transient species produced by laser flash photolysis of iodine and iodoform solutions are reported. The results show that the primary process in the photolysis of iodoform is the formation of atomic iodine.     

Vibronic coupling of pyrene in the first ππ* excited state

The two-photon fluorescence excitation spectrum of pyrene in n-hexane and n-heptane matrices has been measured at 10 K in the region of the first electronic transition (26800–30200 cm^?1). The spectrum consists of a rich number of sharp bands, being in general better resolved in n-hexane than in n-heptane matrix. Shpol'skii multiplets have been observed for the most intense bands. A strong two-photon band dominates the spectrum = 1495 cm^?1 from the 0—0 line and was assigned to B_1u × b_1u = A_g symmetry. Other weaker vibronic origins occur in the spectrum which were correlated to vibrational modes of b_1u, b_2u, b_3u and a_u symmetry. Intense vibronic bands are observed close to the origin of the second electronic transition and were interpreted as combination bands of B_1u × b_1u × b_3g symmetry. A two-photon vibronic theory to account for their intensity is proposed where the electronic moment is linearly expanded in powers of the nuclear displacements.     

Transition metal methylene complexes : III. Methylene (CH2), a carbonyl analogous ligand; crystal structure of μ-methylenebis(carbonyl-η5-cyclopentadienylrhodium)(Rh—Rh

μ-Carbonylbis(carbonyl-ν⁵-cycopentadienylrhodium)(Rh—Rh) reacts with N-methyl-and N-ethyl-N-nitrosourea in boiling benzene to yield the dinuclear, diamagnetic, neutral rhodium complexes μ-methylene- (A) and μ-ethylidenebis(carbonyl-η⁵-cyclopentadienylrhodium)(Rh—Rh) (B), respectively. Deuterium labelled experiments prove the origin of the metal-stabilized methylene ligand to be the alkyl group of the organic precursor. This new method of preparation of transition metal—methylene complexes may be used as an alternative to the commonly used diazo method; the latter method was shown to work with diazodiethylmalonate and dicarbonyl-η⁵-cyclopentadienylrhodium, the reaction yielding μ-bis(ethoxycarbonyl)methylenebis(carbonyl-η⁵-cyclopentadienylrhodium)(Rh—Rh).Compound A crystallizes in the triclinic system, P$\text{1}$, and with cell constants of a 803.42(5), b 909.98(6), c 938.81(2) pm, α 74.402(3), β81.923(3), and γ 83.685(6)°. The unit cell volume and the calculated density are 651.6 ų and 2.069 g cm^-3, for one molecule in the asymmetric unit. The molecular geometry of μ-CH₂[η⁵-C₅H₅Rh(CO)]₂ was established from 2718 unique reflections collected with a computer-controlled diffractometer and refined to a final R(F) = 0.0379. The molecular parameters derived from the single-crystal X-ray study conform to a remarkable degree with those found for μ-CO[η⁵-C₅H₅Rh(CO)]₂. Thus, the bridging ligands CH₂ and CO seem to be analogous in their effects on the structural characteristics of the molecular framework of the two molecules.     

A high pressure differential thermal analysis apparatus

A high pressure differential thermal analysis apparatus is described which is capable of operation in the pressure range from 1-600 atm of nitrogen gas and at temperatures from 25 to 500°C. Use of the apparatus is illustrated by the deaquation reactions of CuCl₂·2H₂0 and CoSO₄·7H₂O at pressures from 1 to 69 atm.     

Determination of the rare-earth elements in geological materials by thin-film X-ray fluorescence and inductively-coupled plasma atomic-emission spectrometry

Thin-film XRF and ICP-AES analytical procedures for the determination of the rare-earth elements (REE) in rocks, involving preconcentration by ion-exchange and co-precipitation with Fe(OH)(3) for thin-film preparation, and matrix modification, are described. The REE in five international reference rocks have been determined, with correction for spectral line overlap whenever necessary. The results obtained by using X-ray fluorescence spectrometry compare well with those of inductively-coupled plasma atomic-emission spectrometry, and with other values reported in the literature.     

Interpretation of the vibrational spectra of methylglyoxal and biacetyl in their first singlet excited electronic states

Laser-induced fluorescence spectra for the first allowed electronic transition (22125 cm^?1) of methylglyoxal (CH₃COCHO) and its perdeutero analog (CD₃COCDO) in a supersonic nozzle beam are quantitatively represented assuming that the potential function governing the CH₃(CD₃) rotation is changed during the transition. In the excited state the potential function is ternary (V₁ = 95 (1 + cos 3θ)cm^?1) as in the fundamental state (V₀ = 134.5 (1 - cos 3θ)cm^?1), but the minima are shifted by an angle of π/3. The spectrum of biacetyl (CH₃COCH₃CO) can be reproduced assuming two uncoupled methyl groups undergoing similar conformational changes during the electronic transition (the estimated potential function is V₁ = 117.5 (1 + cos 3θ) cm^?1 for each methyl group), in perfect agreement with the most recent assignment of the 0-0 transition. These results are consistent with ab initio calculations for the fundamental and first excited singlet states.     

A high pressure electrical conductivity apparatus

A high pressure electrical conductivity (EC) apparatus. capable of operation at pressures from 1 to 170 atm in the temperature range from 25 to 500°C, is described. The effects of the sample holder geometry, pressure, and sample packing on the resulting EC curves are given. Operation of the apparatus is illustrated by the deaquation reactions of BaCI₂·2H₂0.     

Analysis of the decay of picosecond fluorescence in semiconductors: Criteria for the presumption of electroneutrality during the decay of an exponential electron-hole profile

When an exponential profile of electron-hole pairs is photogenerated (in a semiconductor) with a delta-function light pulse, unequal diffusion coefficients of holes and electrons (i.e. D_e≠ D_h) effect deviations from electroneutrality as electrons and holes diffuse into the bulk semiconductor. These deviations will in turn effect errors in the analysis of data (e.g. time resolved fluorescence) when using theory based on the presumption of electroneutrality. We deduce here the experimental conditions required for an effective electroneutrality to be maintained during the course of an experiment. Analyses were carried out using computer simulations without the presumption of electroneutrality and the analytic solution with the presumption of electroneutrality. The differences in the measured fluorescences predicted by the two computations are characterized as a function of a variety of experimental parameters and physical properties: intensity (of the excitation pulse), the absorption of the exciting and emitted light, the the ratio D_h/D_e, bulk dielectric constant of the semiconductor, bulk and surface recombination kinetics. It is shown that a conditon of adequate electroneutrality can be effectively attained when a well defined a minimum number of electron-hole pairs is generated; an upper limit of the number of e^?–k⁺ pairs is also established in order to avoid an intolerable temperature pulse.     

A mechanism for the heat-induced fluorescence of coumaphos and related compounds and the identification of their metabolites in water.

A simple method is proposed for the identification and determination of Potasan in technical coumaphos. The major fluorescent products of coumaphos and Potasan, after heat treatment on t.l.c., are identified as chlorferone and 4-methylumbelliferone, respectively, by i.r., m.s., t.l.c. and fluorescence spectral data. In water, coumaphos degrades into Coroxon, the oxygen analog, and chlorferone, the hydrolysis product. These three compounds can be determined simultaneously on the same chromatogram after extraction from water.     

The vapor-pressure isotope effect for (CH3)2CO and (CD3)2CO from 206 to 333 K

Isotopic vapor-pressure differences between (CH₃)₂CO and (CD₃)₂CO have been measured by differential capacitance manometry. When combined with available absolute vapor pressures for (CH₃)₂CO the results may be expressed (206 to 333 K) as:

$\text{1n}\text{(}\text{p}{}_{\mathrm{H}}\text{p}{}_{\mathrm{D}}\text{) = 3642.6(K/T)}{}^2\text{? 22.205(K/T) + 0.01129}$

     

Vapor pressure measurements of ferrocene,mono- and 1,1′-di-acetyl ferrocene

By using different techniques the vapor pressure of ferrocene, mono-acetyl ferrocene and 1,1′-di-acetyl ferrocene was measured. The following pressure—temperature equations were derived ferrocene log P(kPa)= 9.78 ± 0.14 ? (3805 ± 46)/T mono-acetyl ferrocene log P(kPa) = 14.83 ± 0.14 ? (5916 ± 48)/T 1,1′-di-acetyl ferrocene log P(kPa) = 8.82 ± 0.11 ? (4289 ± 44)/T By second- and third-law treatment of the vapor data the ΔH⁰_sub,298 = 74.0 ± 2.0 kJ mole^?1 for the sublimation process of ferrocene was calculated and compared with the literature data. For the sublimation enthalpy of mono- and 1,1′-di-acetyl ferrocene the values ΔH⁰_sub,298 = 115.6 ± 2.5 kJ mole^?1 and ΔH⁰_sub,298 = 91.9 ± 2.5 kJ mole^?1 were derived by second-law treatment. Thermal functions of these compounds were also estimated.     

2P12 excited iodine formation in the F + HI reaction

Fluorine atoms produced in a microwave discharge of SF₆ were mixed with HI molecules in a flow system. Groundstate and excited iodine atoms were monitored by measuring the absorption of atomic emission lines from an iodine resonance lamp. A model taking into account the formation of excited iodine atoms through the reactive channel as well as the VE energy transfer process from vibrationally excited HF molecules is discussed. The fraction of excited iodine atoms formed in the reaction is shown to be 0.5.