Thermal decomposition of toluene: Overall rate and branching ratio

The two-channel thermal decomposition of toluene, C₆H₅CH₃ → C₆H₅CH₂ + H (1) and C₆H₅CH₃ → C₆H₅ + CH₃ (2), was investigated in shock tube experiments over the temperature range of 1400-1780 K at a pressure of 1.5 (±0.1) bar. Rate coefficients for reactions (1) and (2) were determined by monitoring benzyl radical (C₆H₅CH₂) absorption at 266 nm during the decomposition of toluene diluted in argon and modeling the temporal behavior of the benzyl concentration with a kinetic model. The first-order rate coefficients determined at a pressure of 1.5 bar are expressed by k₁(T) = 2.09 × 10¹⁵ exp (−87510 [cal/mol]/RT) [s⁻¹] and k₂(T) = 2.66 × 10¹⁶ exp (−97880 [cal/mol]/RT) [s⁻¹]. The resulting branching ratio, k₁/(k₁ + k₂), ranges from 0.8 at 1350 K to 0.6 at 1800 K.     

High-pressure laminar flame speeds and kinetic modeling of carbon monoxide/hydrogen combustion

Laminar flame speeds were accurately measured for CO/H₂/air and CO/H₂/O₂/helium mixtures at different equivalence ratios and mixing ratios by the constant-pressure spherical flame technique for pressures up to 40 atmospheres. A kinetic mechanism based on recently published reaction rate constants is presented to model these measured laminar flame speeds as well as a limited set of other experimental data. The reaction rate constant of CO + HO₂ → CO₂ + OH was determined to be k = 1.15 × 10⁵T^2.278 exp(−17.55 kcal/RT) cm³ mol⁻¹ s⁻¹ at 300-2500 K by ab initio calculations. The kinetic model accurately predicts our measured flame speeds and the non-premixed counterflow ignition temperatures determined in our previous study, as well as homogeneous system data from literature, such as concentration profiles from flow reactor and ignition delay time from shock tube experiments.     

A shock-tube and theory study of the dissociation of acetone and subsequent recombination of methyl radicals

The dissociation of acetone: CH₃COCH₃ → CH₃CO + CH₃, quickly followed by CH₃CO → CH₃ + CO, has been examined with Laser-Schlieren measurements in incident shock waves over 32-717 Torr and 1429-1936 K using 5% acetone dilute in krypton. A few very low pressure experiments (∼10 Torr) were used in a marginal effort to resolve the extremely fast vibrational relaxation of this molecule. This effort was partly motivated as a test for molecular, “roaming methyl” reactions, and also as a source of methyl radicals to test the application of a recent high-temperature mechanism for ethane decomposition [J.H. Kiefer, S. Santhanam, N.K. Srinivasan, R.S. Tranter, S.J. Klippenstein, M.A. Oehlschlaeger, Proc. Combust. Inst. 30 (2005) 1129-1135] on the reverse methyl combination. The gradient profiles show strong initial positive gradients and following negative values fully consistent with methyl radical formation and its following recombination. Thus C-C fission is certainly a large part of the process and molecular channels cannot be responsible for more than 30% of the dissociation. Rates obtained for the C-C fission show strong falloff well fit by variable reaction coordinate transition state theory when combined with a master equation. The calculated barrier is 82.8 kcal/mol, the fitted 〈ΔE〉_down = 400 (T/298) cm⁻¹, similar to what was found in a recent study of C-C fission in acetaldehyde, and the extrapolated k_∞ = 10^25.86 T^−2.72 exp(−87.7 (kcal/mol)/RT), which agrees with the literature rate for CH₃ + CH₃CO. Large negative (exothermic) gradients appearing late from methyl combination are accurately fit in both time of onset and magnitude by the earlier ethane dissociation mechanism. The measured dissociation rates are in close accord with one earlier shock-tube study [K. Sato, Y. Hidaka, Combust. Flame 122 (2000) 291-311], but show much less falloff than the high pressure experiments of Ernst et al. [J. Ernst, K. Spindler, H.Gg. Wagner, Ber. Bunsenges. Phys. Chem. 80 (1976) 645-650].     

Synthesis and utilization of chitin-humic acid hybrid as sorbent for Cr(III)

New types of hybrid material have been synthesized by using four different methods of immobilization of humic acid (HA) on chitin. The most stable hybrid material toward the change of medium acidity was then utilized as sorbent for Cr(III).The HA was extracted from peat soil of Gambut District, South Kalimantan, Indonesia, using the recommended procedure of International Humic Substances Society (IHSS), while the chitin was isolated from crab shell waste through deproteination using 3.5% (w/v) NaOH and followed by removal of inorganic impurities using 1 M HCl. The four methods of immobilization of HA on chitin were (i) Method A: chitin powder (4 g) was gently poured into the stirred solution of 0.4 g HA in 40 mL of 0.01 M NaOH. After overnight stirring, the solid was separated, washed with water, and dried in oven at 70 °C. (ii) Method B: gelatinous chitin (40 g) in 250 mL of 0.5 M HCl was reacted with HA (4 g) in 500 mL of 0.5 M NaOH and aged for 24 h. The product was washed with water and dried. (iii) Method C: HA powder (0.5 g) was mixed with the stirred gel of chitin (2.5 g) in 60 mL of CaCl₂ saturated methanol and the mixture was then washed with the mixed solution of 25 mL of 2 M sodium citrate and ethylene glycol 1:1. The solid was separated, washed with water, and dried. (iv) Method D: the solution of HA (0.056 g) in 10 mL of 0.01 M NaOH was reacted with the gel of chitin (0.2 g) in 10 mL of CaCl₂ saturated methanol. After 24 h stirring, the solid was separated from the reaction medium, washed with the mixed solution of 2 M sodium citrate and ethylene glycol 1:1, and followed by washing with water and drying. Parameters investigated in this study consisted of the stability test of the immobilized HA, as well as the rate constant (k₁), capacity (b), and energy (E) of sorption as well as the rate constant of desorption (k₋₁). The k₁ and k₋₁ were determined according to a kinetic model of first order sorption reaching equilibrium, while the b and E were determined according to the Langmuir isotherm model.Compared to HA, Methods, A, C, and D; Method B produced the most stable immobilization of HA on chitin. The hybrid material (Chitin-HA) synthesized through Method B was stable in the acidity range that equivalent to pH 2.0-11.0. At the acidity giving maximum sorption, i.e. pH 5, the presence of immobilized HA on the Chitin-HA enhanced more than three times the k₁ and k₋₁, i.e. from 0.057 min⁻¹ and 8.51 × 10⁻⁴ (min⁻¹) (mol/L) for chitin to 0.183 min⁻¹ and 3.27 × 10⁻³ (min⁻¹) (mol/L) for the Chitin-HA. On the contrary, the presence of HA on Chitin-HA only gave small increase on b and small decrease on E. The values of b and E for Cr(III) on chitin were 1.45 × 10⁻² mol/g and 23.12 kJ/mol, respectively, while those on Chitin-HA were 1.78 × 10⁻² mol/g and 19.95 kJ/mol, respectively.     

On the mechanism of decomposition of the benzyl radical

The C₇H₇ potential energy surface was studied from first principles to determine the benzyl radical decomposition mechanism. The investigated high temperature reaction pathway involves 15 accessible energy wells connected by 25 transition states. The analysis of the potential energy surface, performed determining kinetic constants of each elementary reaction using conventional transition state theory, evidenced that the reaction mechanism has as rate determining step the isomerization of the 1,3-cyclopentadiene, 5-vinyl radical to the 2-cyclopentene,5-ethenylidene radical and that the fastest reaction channel is dissociation to fulvenallene and hydrogen. This is in agreement with the literature evidences reporting that benzyl decomposes to hydrogen and a C₇H₆ species. The benzyl high-pressure decomposition rate constant estimated assuming equilibrium between the rate determining step transition state and benzyl is k₁(T) = 1.44 × 10¹³T^0.453exp(−38400/T) s⁻¹, in good agreement with the literature data. As fulvenallene reactivity is mostly unknown, we investigated its reaction with hydrogen, which has been proposed in the literature as a possible decomposition route. The reaction proceeds fast both backward to form again benzyl and, if hydrogen adds to allene, forward toward the decomposition into the cyclopentadienyl radical and acetylene with high-pressure kinetic constants k₂(T) = 8.82 × 10⁸T^1.20exp(1016/T) and k₃(T) = 1.06 × 10⁸T^1.35exp(1716/T) cm³/mol/s, respectively. The computed rate constants were then inserted in a detailed kinetic mechanism and used to simulate shock tube literature experiments.     

Metal ion-molecule kinetics at combustion temperatures: The reaction of Ca with O2

The high-temperature photochemistry (HTP) technique, previously used for reactions of neutral species, has been adapted to the study of atomic metal ion-molecule reactions. Ca⁺ ions were generated by 193 nm multi-photon photolysis of calcium acetyl acetonate and its pyrolysis fragments. The relative ion concentrations were monitored by laser-induced fluorescence at 393.4 nm. Ar was used as the bath gas. The data for the Ca⁺ + O₂ + M → CaO₂⁺ + M association reaction (1) are fitted by k₁(907-1425 K) = 3.5 × 10⁻³² exp(+3161 K/T) cm⁶ molecule⁻² s⁻¹. Combining with an approximate k₁(296 K) value in the literature leads to k₁(296-1425 K) = 5.8 × 10⁻²² (T/K)^−2.9 exp(−601 K/T) cm⁶ molecule⁻² s⁻¹. Over much of the observed temperature range reaction (1) has much smaller rate coefficients than the corresponding neutral Ca association reaction. Reaction (1) is shown to behave very similarly to the O₂ association reaction with neutral K atoms, with which Ca⁺ is iso-electronic. This suggests that the initial step is ion-pair complex formation of the superoxide Ca²⁺(O₂)⁻, which is also consistent with results from density functional calculations. The k₁ values are rationalized via Troe’s unimolecular formalism, which leads to good accord with the experiments.     

Optical properties of Er in MoO3-Bi2O3-TeO2 glasses

Erbium-doped MoO₃−Bi₂O₃−TeO₂ (MBT) glasses suitable for broadband optical amplifier applications have been fabricated and characterized optically. The maximum phonon band of undoped glasses is at 915 cm⁻¹, and the emission from the Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition locates around 1.53 μm with a full width at half maximum (FWHM) of ∼80 nm. The lifetime and quantum efficiency of the ⁴I_13/2 level are 2.13 ms and ∼90%, respectively. Under the same measurement condition, the upconversion emission intensities at 550 nm in Er³⁺-doped MBT glasses is about 30 times weaker than that in Er³⁺-doped Na₂O−ZnO−TeO₂ (NZT) glasses.     

Ab initio chemical kinetics for the reactions of HNCN with O(P) and O2

The kinetics and mechanisms of the reactions of cyanomidyl radical (HNCN) with oxygen atoms and molecules have been investigated by ab initio calculations with rate constant prediction. The doublet and quartet state potential energy surfaces (PESs) of the two reactions have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df, 2p) level based on geometries optimized at the CCSD/6-311++G(d, p) level. The rate constants for various product channels of the two reactions in the temperature range of 300-3000 K are predicted by variational transition state and RRKM theories. The predicted total rate constants of the O(³P) + HNCN reaction at 760 Torr Ar pressure can be represented by the expressions k_total (O + HNCN) = 3.12 × 10⁻¹⁰ × T^−0.05 exp (−37/T) cm³ molecule⁻¹ s⁻¹ at T = 300-3000 K. The branching ratios of primary channels of the O(³P) + HNCN are predicted: k₁ for producing the NO + CNH accounts for 0.72-0.64, k₂ + k₉ for producing the ³NH + NCO accounts for 0.27-0.32, and k₆ for producing the CN + HNO accounts for 0.01-0.07 in the temperature range studied. Meanwhile, the predicted total rate constants of the O₂ + HNCN reaction at 760 Torr Ar pressure can be represented by the expression, k_total(O₂ + HNCN) = 2.10 × 10⁻¹⁶ × T^1.28exp (−12200/T) cm³ molecule⁻¹ s⁻¹ at T = 300-3000 K. The predicted branching ratio for k₁₁ + k₁₃ producing HO₂ + ³NCN as the primary products accounts for 0.98-1.00 in the temperature range studied.     

Interface control of high-k gate dielectrics on Ge

Important progress has been made in the passivation of Ge/gate dielectric interfaces. One important approach is by thermally oxidized GeO₂ interface and ALD high-k layers, with an interface state density D_it ∼ 2 × 10¹¹ cm⁻² eV⁻¹. Another approach is with an epi-Si/SiO₂ interface, resulting in similar D_it. Hysteresis and V_th shift, however, are still not optimal. Extensive material characterization and theoretical insights help us understanding the root cause of these remaining issues and show the way to improved interface control.     

Hybrid of chitin and humic acid as high performance sorbent for Ni(II)

Hybrid of humic acid (HA) and chitin has been synthesized and the hybrid material (chitin-HA) was then applied as sorbent to adsorb Ni(II). The HA was extracted from peat soil of Gambut District, South Kalimantan, Indonesia, according to the procedure recommended by IHSS (International Humic Substances Society). The chitin was isolated from crab shell waste of sea food restaurants through deproteination using NaOH 3.5% (w/v) and followed by removal of inorganic impurities using HCl 1 M. The synthesis of chitin-HA was performed by reacting gelatinous chitin solution in HCl 0.5 M and HA solution in NaOH 0.5 M. Parameters investigated in this work consists of effect of medium acidity on the sorption, sorption rate (k_s) and desorption rate (k_d) constants, Langmuir (monolayer) and Freundlich (multilayer) sorption capacities, and energy (E) of sorption. The k_s and k_d were determined according to a kinetic model of first order sorption reaching equilibrium, monolayer sorption capacity (b) and energy (E) were determined according to the Langmuir isotherm model, and multilayer sorption capacity (B) was determined based on the Freundlich isotherm model.Sorption of Ni(II) on both chitin and chitin-HA was maximum at pH 8.0. The kinetic expression resulted from the proposed kinetic model has been shown to be more applicable than the commonly known Lagergren equation obtained from the pseudo-first order sorption model. The application of the proposed model revealed that the presence of HA increased the k_s from 0.018 min⁻¹ for chitin to 0.031 min⁻¹ for chitin-HA. As for k_s, the value of b was also bigger in the presence of HA, i.e. 7.42 × 10⁻⁵ mol/g for chitin and 9.93 × 10⁻⁵ mol/g for the chitin-HA. Unlike k_s and b, the value of E slightly decreased from 23.23 to 21.51 kJ/mol for the absence and presence of HA, respectively. It can also be deduced that the presence of HA on chitin contributed more to the additional layer of Ni(II) sorbed on sorbent. Without HA, B for chitin was only 6.17 times higher than b, while with the presence of HA, the enhancement of the sorption capacity from the multilayer (B) to the monolayer (b) was 19.40. The increase of k_s, b, B, and the decrease of E would be very benefit in the real application of chitin-HA for the recovery of Ni(II) from aqueous samples.     

Fourier transform infrared emission spectra of MnH and MnD

Fourier transform infrared emission spectra of MnH and MnD were observed in the ground X⁷Σ⁺ electronic state. The vibration-rotation bands from v = 1 → 0 to v = 3 → 2 for MnH and from v = 1 → 0 to v = 4 → 3 for MnD were recorded at an instrumental resolution of 0.0085 cm⁻¹. Spectroscopic constants were determined for each vibrational level and equilibrium constants were found from a Dunham-type fit. The equilibrium vibrational constant (ω_e) for MnH was found to be 1546.84518(65) cm⁻¹, the equilibrium rotational constant (B_e) is 5.6856789(103) cm⁻¹ and the eqilibrium bond distance (r_e) was determined to be 1.7308601(47) Å.     

Structural evolution of electroless Ni-P coating on Al-12 wt.% Si alloy during heat treatment at high temperatures

The work is concerned with the high-temperature heat treatment of an Al-12 wt.% Si alloy coated by an electroless Ni-P layer. The electroless deposition took place on a pre-treated substrate in a bath containing nickel hypophosphite, nickel lactate and lactic acid. Resulting Ni-P deposit showed a thickness of about 8 μm. The coated samples were heat-treated at 200-550 °C/1-24 h. LM, SEM, EDS and XRD were used to investigate phase transformations. Adherence to the substrate was estimated from the scratch test and microhardness of the heat-treated layers was also measured. It is found that various phase transformations occur, as both temperature and annealing time increase. These include (1) amorphous Ni-P → Ni + Ni₃P, (2) Al + Ni → Al₃Ni, (3) Ni₃P → Ni₁₂P₅ + Ni, (4) Ni₁₂P₅ → Ni₂P + Ni, and (5) Al₃Ni + Ni → Al₃Ni₂. The formation of intermetallic phases, particularly Al₃Ni₂, leads to significant surface hardening, however, too thick layers of intermetallics reduce the adherence to the substrate. Based on the growth kinetics of the intermetallic phases, diffusion coefficients of Ni in Al₃Ni and Al₃Ni₂ at 450-550 °C are estimated as follows: D(Al₃Ni, 450 °C) ≈ 6 × 10⁻¹² cm² s⁻¹, D(Al₃Ni, 550 °C) ≈ 4 × 10⁻¹¹ cm² s⁻¹, D(Al₃Ni₂, 450 °C) ≈ 1 × 10⁻¹² cm² s⁻¹ and D(Al₃Ni₂, 550 °C) ≈ 1 × 10⁻¹¹ cm² s⁻¹. Mechanisms of phase transformations are discussed in relation to the elemental diffusion.     

Pressure dependence of spectral positions and widths of emission lines related to DJ→FJ electronic transitions in Sm ions doped into SrFCl single crystal

The pressure dependence of the peak positions and widths of the fluorescence lines corresponding to the ⁵D_J→⁷F_J electronic transitions in Sm²⁺-doped SrFCl crystals was measured at room temperature (RT) with a diamond anvil cell (DAC) and a high-pressure gas system, using silicone oil and gaseous helium as the pressure-transmitting medium, respectively. At RT and ambient pressure the electronic transitions ⁵D₀→⁷F_J (J= 0, 1, 2, 3) and ⁵D₁→⁷F_J (J=0, 1, 2) in Sm²⁺ ions yielded rather sharp spectral lines peaked at 14490, 14206, 13685, 13012 cm⁻¹ and 15823, 15533, 15012 cm⁻¹, respectively. At pressures up to 45 kbar in the DAC all these peaks shifted linearly to lower energies at the rates −2.36, −2.10, −2.43, −2.22 cm⁻¹/kbar and −2.35, −2.33, −2.47 cm⁻¹/kbar. Under purely hydrostatic gas pressure up to 7 kbar at RT the initial (normal pressure) widths of the ⁵D₀→⁷F₀, ⁵D₀→⁷F₁ and ⁵D₁→⁷F₀ lines having a Lorentzian profile (with corrected FWHM values of 1.55, 5.71 and 1.97 cm⁻¹) decreased linearly with increasing pressure at the rates −0.009(2), −0.077(3) and −0.034(2) cm⁻¹/kbar, respectively. Possible mechanisms of the observed pressure effects are discussed. For further studies of linewidth variations with the pressure, gaseous helium as a best possible high-pressure medium is strongly recommended.     

Ferromagnetism in amorphous Ge1−xMnx grown by low temperature vapor deposition

Magnetic properties of amorphous Ge_1−xMn_x thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge_1−xMn_x thin films are 5.0×10⁻⁴∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge_1−xMn_x thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80-160 K, and saturation magnetization is 35-100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge_1−xMn_x thin films have p-type carrier and hole densities are in the range from 7×10¹⁷ to 2×10²² cm⁻³.     

The bΣ(b0) → XΣ(X10,X21) and aΔ(a2) → X21 transitions of AsBr

Emission spectra of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺,X₂1) and a¹Δ(a2) → X₂1 transitions of AsBr have been measured in the near-infrared spectral region with a Fourier-transform spectrometer. The arsenic bromide radicals were generated in fast-flow systems by reaction of arsenic vapor (As_x) with bromine and were excited by microwave-discharged oxygen. The most prominent features in the spectrum are the Δv = +1,0,−1, and −2 band sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₁0⁺) transition in the range 11 700-12 700 cm⁻¹. With lower intensities, the Δv = 0 and −1 sequences of the b¹Σ⁺(b0⁺) → X³Σ⁻(X₂1) sub-system show up in the same range. Further to the red, between 6000 and 6700 cm⁻¹, the Δv = 0, +1, and −1 sequences of the hitherto unknown a¹Δ(a2) → X₂1 transition are observed. Analyses of medium- and high-resolution spectra have yielded improved molecular constants for the X₁0⁺, X₂1, and b0⁺ states and first values of the electronic energy and the vibrational constants of the a2 state.     

Investigations of meta-stable and post-spinel silicon nitrides

Since the discovery of post-spinel Si₃N₄, its fundamental physical properties are highly required. In this paper, theoretical calculations are performed to investigate the structural and elastic properties of the β-, γ-, wII- and post-spinel Si₃N₄ polymorphs. The calculated ground-state properties compare well with available experiments. The phase transformations of the β-, γ-, wII- and post-spinel phases are investigated by the famous plane-wave pseudo-potential density functional theory. From the elastic constants obtained, we find that β-, γ- and wII-Si₃N₄ are stable at 0 GPa and the post-spinel phase is unstable/stable at 0 GPa/160 GPa. When the high-temperature β→γ transformation is bypassed due to kinetic reasons, β-Si₃N₄ is predicted to undergo a first-order phase transition to a new phase (wII-Si₃N₄). It is found that the transition pressures of β→wII and γ→post-spinel transitions are 20.8 GPa and 152.5 GPa, respectively. The phase boundary of the γ→post-spinel transition can be described as P=152.3631−6.39×10⁻³T+2.01062×10⁻⁵T²−1.93962×10⁻⁹T³. Through the quasi-harmonic approximation, the dependences of heat capacity, entropy, thermal expansion coefficient and the Debye temperature on temperature, are also successfully predicted.     

Single crystal EPR and optical absorption study of Cr doped l-histidine hydrochloride monohydrate

EPR study of the Cr³⁺ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr⁵³ isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.9108±0.0002, g_y=1.9791±0.0002, g_z=2.0389±0.0002, A_x=(252±2)×10⁻⁴ cm⁻¹, A_y=(254±2)×10⁻⁴ cm⁻¹, A_z=(304±2)×10⁻⁴ cm⁻¹ for site I and D=(300±2)×10⁻⁴ cm⁻¹, E=(96±2)×10⁻⁴ cm⁻¹, g_x=1.8543±0.0002, g_y=1.9897±0.0002, g_z=2.0793±0.0002, A_x=(251±2)×10⁻⁴ cm⁻¹, A_y=(257±2)×10⁻⁴ cm⁻¹, A_z=(309±2)×10⁻⁴ cm⁻¹ for site II, respectively. The optical absorption studies of single crystals are also carried out at room temperature in the wavelength range 195-925 nm. Using EPR and optical data, different bonding parameters are calculated and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are: B=636, C=3123, Dq=2039 cm⁻¹, h=1.46 and k=0.21, respectively.     

Influence of moieties for the phase stability, spontaneous polarization and dielectric relaxations in an achiral ferroelectric bent liquid crystal, PBUOB

The occurrence of ferroelelectric phases and influence of chemical moieties in the area of supra-molecular achiral Bent core Liquid Crystals (BLCs) are reviewed. Synthesis of an intermediate/higher homolog of PBnOB series (for n=11), PBUOB, viz. 1,3−Phenyline-Bis(4−UndecylOxy Benzoate), is presented. Smectic LC phases exhibited by PBUOB are characterized by Polarized Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and Spontaneous Polarization (P_S) techniques. Observations infer a bi-variant FE LC smectic phase occurrence, viz., isotropic→B₂(FE)→B₅(FE)→solid phases in cooling and solid→B₅→isotropic phases in heating scans. Occurrence of B₂ phase is monotropic (in cooling), while B₅ phase is enantiotropic. I-B₂ and B₂-B₅ phase transitions are found to be of first order nature. The FE phases possess a moderate P_S value of ∼40 nC cm⁻². Transition temperatures from dielectric studies agree with those from TM and DSC. Two modes of relaxations are observed, viz., a slow scissor mode at ∼1 kHz and a fast mode at ∼1 MHz. Anisotropic Dipolar Model is proposed to explain the reorientation mechanism. Arrhenius shifts of Relaxation Frequency (f_R) show differing activation energies for two modes, i.e., 0.11 and 0.98 eV; 0.25 and 1.18 eV in B₂ and B₅ phases, respectively. Temperature variation of dielectric increment Δε and α-parameter LC phases reveals the relative fixture of dipole moment in polar smectic layers. An analytical study for the thermal stability, P_S and f_R in the FE phases is presented with respect to the constitution and configuration of moieties in BLCs.     

Surface mass diffusion and step stiffness on an anisotropic surface; Mo(0 1 1)

Results of step fluctuation experiments for Mo(0 1 1), using low-energy electron microscopy, are re-examined using recently developed procedures that offer accurate coefficients of surface mass diffusion. By these means, surface diffusion D_s is documented at T/T_m ∼ 0.5, while the crossover to relaxation driven by bulk vacancy diffusion is inferred for T/T_m ∼ 0.6. Here, T_m is the melting temperature T_m = 2896 K. We obtain D_s = 4 × 10⁻⁴ exp(−1.13 eV/k_BT) cm²/s for the temperature interval 1080-1680 K. Possible indications of diffusion along step edges appear for T/T_m ∼ 0.4. The same measurements of step fluctuation amplitudes determine also the step stiffness, which by symmetry is anisotropic on Mo(0 1 1). It is shown that three independent procedures yield mutually consistent step stiffness anisotropies. These are (1) step fluctuation amplitudes; (2) step relaxation rate anisotropies; and (3) the observed anisotropies of islands in equilibrium on the Mo(0 1 1) surface. The magnitude of the step stiffness obtained from step edge relaxation is consistent with earlier measurements that determine diffusion from grain boundary grooving.     

The absorption spectrum of water between 13 540 and 14 070 cm: ICLAS detection of weak lines and a complete line list

The absorption spectrum of water vapor has been investigated by Intracavity Laser Absorption Spectroscopy (ICLAS) between 13 540 and 14 070 cm⁻¹. This spectrum is dominated by relatively strong transitions of the 4δ polyad of vibrational states. The achieved sensitivity - on the order of α_min ∼ 10⁻⁹ cm⁻¹ - has allowed one to newly measure 222 very weak transitions with intensities down to 5 × 10⁻²⁸ cm/molecule at 296 K. Fifty new or corrected H₂¹⁶O energy levels belonging to a total of 13 vibrational states could be determined from the rovibrational analysis based on variational calculations by Schwenke and Partridge. The previous investigations in the region by Fourier Transform Spectroscopy were critically evaluated and used to construct the best to date set of energy levels accessed by transitions in the considered region. All the rovibrational transitions reaching these upper energy levels and having intensities larger than 4.0 × 10⁻²⁸ cm/mol were calculated. In the resulting line list, the positions at the level of experimental accuracy were augmented with variational intensities leading to the most complete line list for water in normal isotopic abundance in the 13 500-14 100 cm⁻¹ region.