Single-crystal reflection and Raman spectra of the polydiacetylene THD

The 298 K. Raman and reflection spectra of the polydiacetylene THD, a close structural variant of DCHD, are presented. The polymer double- and triple-bond stretch frequencies are 1485 and 2111 cm⁻¹, respectively, and the lowest electronic transition peaks at 17600 cm⁻¹. The reflection spectrum is more reminiscent of the polydiacetylene TCDU than DCHD.     

Electroreflectance studies on the excitons in PTS and DCHD single crystals

In polydiacetylene single crystals of PTS [poly-2,4-hexadiyne-1,6-diol-bis(p-toluene sulfonate)] and of DCHD [poly-1,6-di(N-carbazolyl)-2, 4-hexadiyne] electric field modulated reflectance spectra in the range of the π-π* excitations of the polymer indicate considerable delocalization of the electrons along the chain. Shape and size of the excitonic electroreflectance spectra are determined by a large charge transfer component of the excitons. Evaluation of the spectra yields about 20% and 40% charge transfer with excitation to neighbouring π bonds in PTS and DCHD, respectively. Large differences occur in electroreflectance in the range of vibronic excitons pointing to pronounced coupling of the carbazole side group in DCHD to the π electrons of the chain. At higher energy, ?0.48 eV above the lowest exciton transition in both polymers a large electroreflectance signal is observed which is attributed to a band transition.     

Aligning poly[1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne] crystalline fibers as conducting channels for transistor applications

Aligned crystallites of 1,6‐di‐(N‐carbazolyl)‐2,4‐hexadiyne (DCHD) were prepared on the phenyltrichlorosilane‐modified SiO₂/Si surface using the brush‐coating method. The length and width as well as the orientation of the crystallites depend on the coating speed. At a lower coating speed of 0.2 ~ 0.3 mm/s, well‐separated fibers with a width of 1–2 μm and a length of hundreds of μm were grown along the coating direction. Higher speeds resulted in shorter fibers together with randomly oriented tiny crystallites appearing in between. The diacetylene crystallites upon UV irradiation gave polydiacetylene fibers with deformations along the fiber axis. The poly(ene‐yne) backbones were shown to align along the fiber axes. With these poly‐DCHD fibers as a conducting channel for transistor fabrication, a highest field‐effect mobility of 0.039 cm²/Vs was obtained.     

The lowest quartet state of copper porphin: Zeeman experiments at 4.2 K

Zeeman experiments in a magnetic field of 75 kG on copper porphin in a single crystal of n-octane prove the lowest metastable state to be a quartet as predicted by Gouterman and colleagues. In zero magnetic field this quartet is split into two degenerate pairs, the ±$\text{1}\text{2}$ components lying at about 0.7 cm^?1 higher energy than the ±$\text{3}\text{2}$ components.     

Infrared high temperature spectra of aluminium chloride and related species

Isothermal cells of nickel with diamon windows were used to study various melts and vapours by infrared emission, transmission and reflectance techniques in the 860 to 300 K range with an evacuable Fourier transform spectrometer.IR vapour spectra of AlX₃ (X = Cl, Br, I) and GaCl₃ in transmission and emission were measured between 700 and 50 cm^?1. A comparable signal/noise ratio between the transmission and emission spectra was obtained above 200 cm^?1, below 200 cm^?1 the transmission spectra had better quality. The dimer and monemer spectra were assigned in terms of $\text{D}$_2h and $\text{D}$_3h symmetry, respectively, and compared with earlier Raman and IR matrix isolation data.Emission spectra of chloroaluminates AlkAlCl₄ (Alk = Li, Na, K, Rb, Cs) were recorded as melts between 1500 and 50 cm^?1. Increasing distortion of the tetrahedral AlCl^?₄ ion in the series Cs<Rb<K<Na<Li was observed. Emission spectra of AlkAl₂Cl₇ (Alk = Li, Na, K, Cs) indicate $\text{D}$_3d symmetry for Al₂Cl^?₇ with a linear Al-Cl-Al bridge as proposed from earlier Raman data. As a demonstration of reflectance technique an IR spectrum of ZnAl₂Cl₈ at ambient temperature is presented.     

Energy levels of iodine monochloride near the first dissociation limit

Absorption transitions to vibrational levels close to the A state dissociation limit of ICI have been examined using a two-photon sequential absorption technique. The discrete rotational structures of I³⁷ Cl bands to within 0.7 cm^?1 of the limit have been selectively excited and analysed. A value of 17557.514 ± 0.030 cm^?1 has been obtained for the I(²P^o_{$\text{3}\text{2}$}) + Cl(²P^o_{$\text{3}\text{2}$}) dissociation energy D_e, relative to the minimum of the ICI ground state potential well. The two-photon technique can be used to excite and display separately the high resolution absorption spectra of different isotopic species of a molecule which are contained in a mixture.     

The ligand-field spectrum of Fe3+ in garnets

The ligand-field spectra of garnets bearing Fe³⁺ exclusively at the octahedral as well as at the octahedral and tetrahedral sites have been studied at energies between 8000 and 30 000 cm^?1. The absorption bands up to 28 000 cm^?1 have been assigned by comparison of experimental and calculated transition energies obtained by a complete solution of the d⁵ energy matrices. The Racah parameters of Fe³⁺ in both positions have been reinterpreted using a constant $\text{C}\text{B}$ ratio evaluated from the gaseous Fe³⁺ ion. It was found that the octahedral B parameters are always larger than the tetrahedral ones. The results are consistent with isomer shifts of ⁵⁷Fe and the observed structural features in oxide garnets.     

Un nouveau conducteur ionique (LaO)AgS

The compound (LaO)AgS is prepared by reaction of Ag₂S and La₂O₂S, in the presence of a small proportion of iodine, between 580 and 640°C. The cell is tetragonal, space group $\text{P4}\text{n}$ or $\text{P4}\text{nmm}$. The structure is not known, but is probably formed by alternating (LaO) and (AgS) sheets. The electric conductivity is determined by the complex impedance method, with blocking electrode, and by emf measurements; it is mainly ionic, with σ = 10^?3 to 10^?1 Ω^?1 cm^?1 between 25 and 250°C. The activation energy is 0.195 ± 0.005 eV.     

Direct absorption measurement of the spin—orbit splitting of the ground state in atomic fluorine

We have measured the three hyperfine components of the spin—orbit split (²P_{$\text{3}\text{2}$} → ²P_{$\text{1}\text{2}$}) ground state in atomic fluorine by diode laser absorption spectroscopy. The measurement improves the accuracy of the two lines previously reported (404.175 and 403.969 cm^?1), with the third line at 404.210 cm^?1. This confirms the spacing of the hyperfine components measured by EPR, and establishes diode laser absorption as a viable technique for determining F-atom concentrations.     

Synthesis and properties of a new polydiacetylene: Poly[1,6-di(N-carbazolyl)-2,4-hexadiyne]

The solid-state synthesis and properties are reported for a new polydiacetylene: poly[1,6-di(N-carbazolyl)-2,4-hexadiyne]. The monomer crystals polymerize quantitatively with γ irradiation or thermal annealing. An Autocatalytic effect is observed in both γ-ray polymerization and thermal polymerization and is attributed to an increase in chain propagation length at about 5% conversion. The activation energy for thermal polymerization is about 25 kcal/mole, independent of the degree of conversion to polymer. The exceptional thermal stability of the polymer crystals allowed a thermomechanical analysis over a large temperature range, ?50 to 300°C. With increasing temperature, the polymer contracts in the chain direction linearly with temperature over the entire range, yielding a thermal expansion coefficient of (?2.32 ± 0.02) × 10^?5°C^?1. Photoconductivity action spectra are reported for the polymer crystals. The energies for the photoconductivity onset (ca. 2.3 eV) and for the lowest energy optical transition (1.89 eV) are the lowest reported for the polydiacetylenes. The photoconduction onset is blue-shifted with respect to optical absorption—a result which is consistent with the excitonic assignment for the lowest energy optical transition in the polydiacetylenes.     

1H NMR spectra of 1-alkyl-1,2,3,4-tetrahydro-2-oxo-3-azocine-carboxylic acid derivatives and their analogues

¹H NMR spectra of 1-alkyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylates and -carbonitriles indicated that the geminal protons at the 1-α-position were located in noneqnivalent magnetic environments. The difference in the chemical shifts amounted to as much as 0.73 ppm in the case of methyl 1-ethyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate at 26°, and the free energy of activation for the coalescence was estimated to be larger than 23 $\text{kcal}\text{mol}$. The same type of nonequivalence and coalescence phenomena were also observed even with dimethyl protons at the 1-γ-position of 1-isobutyl-1,2,3,4-tetrahydro-2-oxo-3-azocinecarboxylate (ΔG^≠_c = 19 $\text{kcal}\text{mol}$). The situation was hardly affected by the reduction of the CC double bonds. The nonequivalence was not observed, however, if the substituent at the 3-position was absent. Therefore, these novel ¹H NMR spectra of 1-alkyl protons in the title compounds were concluded to be due to strong coupling between the restricted rotation around N(1)—C(α) bond and inversion of the 2-oxoazocine ring which required high energy of activation.     

Observation of new bands in the N2 Herman infrared system and kinetic study of its formation in a pulsed-discharge apparatus

Four new bands of the unassigned N₂ Herman infrared system (HIR) are observed in a pulsed-discharge apparatus. The upper HIR state is produced by the N₂(A) + N₂(A) energy pooling reaction which is studied by time-resolved spectroscopy; its production rate constant is found to be ?4 × 10^?11 cm³ molecule^?1 s^?1 and its energy $\text{}\text{?}$12eV.     

Yield of I(2Psol:12) in the photodissociation of CH2I2

The production of I(²P_{$\text{1}\text{2}$}) in the photolysis of CH₂I₂ has been studied optoacoustically at excitation wavelengths between 365.5 and 247.5 nm. Bands found at 32200 and 47000 cm^?1 correlate with I(²P_{$\text{3}\text{2}$}) whilst those at 34700 and 40100 cm^?1, which correlate with I(²P_{$\text{1}\text{2}$}), give final ²P_{$\text{3}\text{2}$}/²P_{$\text{1}\text{2}$} ratios of 1.75 and 1.1, respectively, after curve crossing.     

A study of the near infrared emission bands of the hydroperoxyl radical at medium resolution

Emissions of the hydroperoxyl radical HO₂ in the spectral range from 1.0 to 1.6 μm were studied at low and medium resolution. The resolved spectrum shows the expected parallel band structure for the vibrational ovetone transition ²A″ (200-000); in the case of the vibronic transitions ²A′, 000 → ²A″, 000 and ²A′, 001 → ²A″, 000, however, comparison of experimental and computer simulated spectra shows that there also occur intense subbands with ΔK = 0, in addition to the ordinary ΔK = ± 1 transitions. The cause for the break-down of the type-C selection rule is not well known. In the reaction system of ethylene with discharged oxygen vibronic bands could be observed originating from ²A′ levels up to at least ν′₃ = 6. The most probable excitation mechanism for these high vibronic levels is the chemiluminescent reaction HCO + O₂ (¹Δ_g) → HO₂(²A′, 00ν′₂) + CO. From the computer fits to the spectra of HO₂ and DO₂ at medium resolution the origins of the 000-000 bands and the fundamental frequencies $\text{ν}$_3′ of the excited ²A′ state could be determined; the values are $\text{ν}$_o(HO₂)=7028 ± 3 cm^?1, $\text{ν}$_o(DO₂)=7034 ± 8 cm^?, $\text{ν}$_3′(HO₂)=927 ± 10 cm^?, and $\text{ν}$_3′(DO₂)=940 ± 28 cm^?1.     

The observation of fine-structure transitions in the LMR spectrum of the SeD radical at 5.6 μm

Magnetic and electric dipole transitions between the ²Π_{$\text{1}\text{2}$} and ²Π_{$\text{3}\text{2}$} components of the ground state of SeD have been observed at 1770 cm^?1 in an LMR experiment using a CO laser. The measurements have been combined with other data from the EPR and far-infrared LMR spectra to determine parameters in the effective hamiltonian. A combination of these results with the analogous ones for SeH provides a determination of fundamental parameters relating to the spin-orbit and spin-rotation interactions.     

Collisional energy transfer to methane by octupole coupliing

A linear molecule or one electron atom interacting with a tetrahedral molecule is considered. Formulae are presented for various rotationally averaged E → R and V → R first order transition probabilities arising from dipole-octupole (R^?5) and quadrupole-octupole (R^?6) coupling. Relatively large amounts of rotational energy can be transferred in first order (ΔJ ? 3). With CH₄ as the octupolar partner, energy transfer upto 350 cm^?1 at room temperature is shown to proceed very efficiently. For the 5²P_{$\text{3}\text{2}$} → 5²P_{$\text{1}\text{2}$} transition in Rb, σ_qu is calculated to be ? 28 A² in quite good agreement with experiment and using an independent value of the octupole moment of CH₄. Energy transfer above 350 cm^?1 becomes rapidly less efficient. Among V → R transfer processes in the 500–700 cm^?1 range, the long range mechanism is almost certainly not the dominant one in the relaxation of CO₂⁺ (010) by CH₄ (σ_calc ≈ 10^?3 σ_obs) but will be important in the relaxation of SO₂.     

The importance of spin relaxation in the delayed fluorescence of molecular crystals

Deactivation rate constants of spin-orbital excited Br atoms in the reactions Br(²P_{$\text{1}\text{2}$}) + O₂ → Br(²P_{$\text{3}\text{2}$}) + O₂ (k₁), and Br(²P_{$\text{1}\text{2}$}) + NO → Br(²P_{$\text{3}\text{2}$}) + NO (k₄) have been measured with a photodissociative IBr laser on the electronic transition ²P_{$\text{1}\text{2}$}?²P_{$\text{3}\text{2}$} in the Br atom (λ = 2.7 μm). The values obtained are (6.4 ± 1.8) × 10^?14 cm³ s^?1 and (1.9 ± 0.6) × 10^?12 cm³ s^?1, respectively. Comparison with published data leads to the conclusion that, contrary to a widely accepted point of view, the high rate constants for the quenching of excited halogen atoms are due to resonant energy transfer processes and not to the paramagnetic nature of the quencher.     

Polyamides with piperazine units in the polymer chain—I: Crystal structure and molecular packing of poly(1,4 piperazine-trans-4-octen-1,8 dioyl)

The crystal structure of poly(1–4 piperazine-trans-4-octen-1,8 dioyl) has been determined from X-ray fibre spectra. The unit cell parameters are: $\text{α=4.54 A; b = 10.00}\text{A}\text{?}\text{; c =13.50}\text{A}\text{?}$ (fibre axis) β = 110°15′ space group P2₁/n. Z =2, d_x = 1.28 g/cm³ (d_obs = 1.23 g/cm³).The chain symmetry is ti. The value of β ≠ 90° is determined by the necessity of suitably packing the neighbouring paraffinic chains and piperazine rings, at the shortest possible distance. The mode of packing of the paraffinic portions of the chains, in the a direction, is reminiscent of the analogous situation met for polyalkenamers (even series).     

Cohesive energy densities of polyethers: Poly(hexamethylene oxide)

The solubility parameter of poly(hexamethylene oxide) has been estimated by measuring solution viscosities and by turbidimetric titrations in a series of solvents. From both experimental methods, a value of $\text{δ}{}_{\mathrm{<mtext>p</mtext>}}\text{= 33.9}\text{J}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$ ($\text{8.1}\text{cal}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{cm}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}$) was obtained, whence the cohesive energy density is 274.5 J cm^?3 (65.6 cal cm^?3). These experimental values are compared with those calculated by empirical methods.     

Synthesis and performance of proton conducting chitosan/NH4Cl electrolyte

The polymer electrolytes based on chitosan and ammonium chloride were prepared by solution casting technique and the properties were studied. The addition of ammonium chloride results in: (1) the enhancement of the amorphous nature of the polymer electrolytes; (2) the shift of the absorption bands of amino group at 1566 cm^?1 and the carbonyl group at 1640 cm^?1 towards lower wave number, and the appearance of a new absorption band at 1759 cm^?1; (3) a decrease of the glass transition temperature. The 20 wt % ammonium chloride doped polymer electrolyte has the best room temperature electric property, the lowest activation energy and the highest ionic conductivity. Placing the as‐prepared polymer electrolyte in a dryer is adverse for the sample's moisture content, and results in higher activation energy and lower ionic conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 260–266, 2010