Far-infrared absorption spectrum of the CH4-H2 gaseous mixture

The rototranslational absorption spectrum of the CH₄-H₂ gaseous mixture has been measured at five different temperatures from 296 to 140 K, in the frequency range 150–850 cm^-1. The absorption spectra due to the CH₄-H₂ interactions have been analyzed considering only the quadrupolar induction of H₂ on CH₄ and the octupolar and hexadecapolar inductions of CH₄ on H₂. Under this assumption, the experimental data have been well accounted for, thereby providing a reliable way of predicting the CH₄-H₂ spectrum in a wide temperature range.     

Nonlinear absorption of new mesoionic compounds

The nonlinear absorption of new mesoionic compounds (MIC) was investigated using nanosecond laser pulses with wavelengths at 570, 605 and 618 nm. Nonlinear absorption cross-sections, σ₂ ≈ 10⁻⁴⁵ cm⁴ s/photon, larger than any recorded in the literature, were obtained due to the introduction of p-CF₃-C₆H₄ electron-acceptor and p-CH₃-C₆H₄ or p-CH(CH₃)₂-C₆H₄ electron-donor groups in the MIC ring. The large values of σ₂, the ease of synthesis of these compounds and their marked stability, make them promising candidates for photonic applications.     

Gastrennung mit Hilfe des Zirkulations-Diffusions-Verfahrens Teil 2: Trennung von stabilen Isotopen und technischen Gasmischungen durch Massen- bzw. “Sweep”-Diffusion

Es wurde ein Massendiffusionsrohr konstruiert und mit Wasserdampf als Treibmittel zur Abtrennung von ¹³CH₄ aus Methan-gas mit natürlicher Isotopenzusammensetzung (¹³CH₄-Anteil: 1,06%) eingesetzt. Der maximale Trennfaktor betrug 1,13. Mit den experimentellen Ergebnissen und Ansätzen aus der Literatur wurde eine Kaskade für die Gewinnung von 1 g ¹³CH₄ pro Tag (90%ige Reinheit) berechnet.

Mit einem zweiten Trennrohr, das nach dem Prinzip der “Sweep”-Diffusion gebaut wurde, erfolgten Trennversuche an H₂-N₂- und H₂-CH₄-Gasmischungen. Es wird die Berechnung einer Trennanlage zur Geiwinnung von 500 m³/h Wasserstoff (90%ig) aus einer H₂-CH₄-Mischung diskutiert. Ein technischer Einsatz der “Sweep”-Diffusion scheint günstig, wenn nur kleinere Gasmengen anfallen und Abdampf zur Verfügung steht.     

Spectrofluorometric investigation of salicylal- dithiocarbazinic acid esters

The fluorescent properties of salicylaldithiocarbazinic esters which can be described by RR¹C= N-NH-CSSR² (where R = 0HO-C₆H₄; R¹ = H or CH₃; R² =CH₃, C₆H₅-CH₂ or p-C1-C₆H₄-CH₂) have been investigated.The investigations were made in DMF, in different DMF-water mixtures, and in aqueous media. It could be stated that the change of the R² group has an unimportant effect on the intensity of fluorescence and on the excitation and emission spectra in all examined solvents. But an important effect is caused by the change of the group R¹. As in DMF solution, only the excitation spectrum changes on substituting R¹ = H by R¹ = CH₃, in DMF: water i.e. aqueous media, the change in the intensity of fluorescence, too, is very great.In the case of R¹ = H, the intensity of fluorescence is about five times greater than in R¹ = CH₃. The intensity of fluorescence can be increased, if an electrophil substituent is put into the place of group R¹.     

Multi-species laser absorption sensors for in situ monitoring of syngas composition

Tunable diode laser absorption spectroscopy sensors for detection of CO, CO₂, CH₄ and H₂O at elevated pressures in mixtures of synthesis gas (syngas: products of coal and/or biomass gasification) were developed and tested. Wavelength modulation spectroscopy (WMS) with 1f-normalized 2f detection was employed. Fiber-coupled DFB diode lasers operating at 2325, 2017, 2290 and 1352 nm were used for simultaneously measuring CO, CO₂, CH₄ and H₂O, respectively. Criteria for the selection of transitions were developed, and transitions were selected to optimize the signal and minimize interference from other species. For quantitative WMS measurements, the collision-broadening coefficients of the selected transitions were determined for collisions with possible syngas components, namely CO, CO₂, CH₄, H₂O, N₂ and H₂. Sample measurements were performed for each species in gas cells at a temperature of 25 °C up to pressures of 20 atm. To validate the sensor performance, the composition of synthetic syngas was determined by the absorption sensor and compared with the known values. A method of estimating the lower heating value and Wobbe index of the syngas mixture from these measurements was also demonstrated.     

Ultrasound irradiation promotes the synthesis of new 1,2,4-triazolo[1,5-a]pyrimidine

Ultrasonic irradiation was used in the synthesis of a series of novel 1,2,4-triazolo[1,5-a]pyrimidines. The products were synthetized from the cyclocondensation reaction of 1,1,1-trifluoro-4-metoxy-3-alken-2-one [CF₃C(O)CHC(R)OMe, where R = Ph, 4-F-C₆H₄, 4-Br-C₆H₄, 4-I-C₆H₄, 4-CH₃-C₆H₄, 4-CH₃O-C₆H₄, Thien-2-yl, Biphen-4-yl] or β-enaminones [RC(O)CHCHNMe₂, where R = Ph, 4-F-C₆H_4, 4-Br-C₆H_4, 4-I-C₆H_4, 4-CH₃-C₆H₄, 4-CH₃O-C₆H₄, 4-NO₂-C₆H₄, Thien-2-yl, Biphen-4-yl, Naphth-2-yl, Pyrrol-2-yl, CCl₃] with 5-amino-1,2,4-triazole in acetic acid at 99 °C with 5–17 min of ultrasound irradiation. This methodology has shown several advantages, such as shorter reaction times, mild conditions, high regioselectivity, and excellent yields, when compared with conventional thermal heating (oil bath).     

Dissociation mechanism of electronically excited CHn (n = 3–5) neutrals formed by near-resonant neutralization using charge inversion mass spectrometry

Charge inversion mass spectrometry was used to produce the electronically excited species CH_n (n=3–5) from their corresponding positive ions by neutralization with an alkali metal target, and then to subsequently detect and mass-analyze the negative ions formed from the neutral fragments produced from the dissociation of the excited neutrals. The trapezoidal shape and the intensity of the peak associated with CH₂^- ions in the charge inversion spectrum of CH₃⁺ ions indicated that the CH₃ neutrals dissociated mainly into CH₂ + H without a large activation barrier. The most intense peak in the spectrum of CH₄⁺ ions was that associated with CH₂^- ions, and this peak comprised a combination of both trapezoidal and triangular shaped peaks. The trapezoidal shaped peak was attributed to CH₂^- ions resulting from direct dissociation of CH₄ into CH₂ + H₂. The concurrent dissociation of CH₄ into CH₃ + H was followed by the further subsequent dissociation of the deformed CH₃ fragments into CH₂ + H, and this was proposed to be the origin of the triangular shaped component of the CH₂^- peak. In the spectrum of CH₅⁺ ions, the CH₃^- peak was much less intense than the CH₂^- peak, which was proposed to be the result of the geometry of the CH₃, formed from the dissociation of CH₅ into CH₃ + H₂,being substantially distorted from the D_3h symmetry, leading to its further subsequent dissociation.     

Analysis of newly synthesized disulfides of aryldithiocarbonates and vanadium(V) and niobium(V) complexes of aryldithiocarbonates based on spectroscopic,thermogravimetric, SEM and DFT studies

ABSTRACT

Oxidation of the sodium salt of 2-methyl, 3-methyl, 4-methyl and 4-chloro-3-methylphenyldithiocarbonic acid by I₂ affords the disulfides of respective dithiocarbonates [(ArOCS₂)₂] (Ar?=?2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃. Vanadium(V) and Niobium(V) complexes of 2-methyl, 3-methyl, 4-methyl and 4-chloro-3-methylphenyldithiocarbonates have also been synthesised by one-step synthetic route. The metal salt (VOCl₃ and NbCl₅) were reacted with 2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃OCS₂Na in 1:2 stoichiometric molar ratio yielding the complexes corresponding to the molecular formula [(ArOCS₂)₂VO(Cl)] and [(ArOCS₂)₂NbCl₃] [Ar?=?2-CH₃C₆H₄, 3-CH₃C₆H₄, 4-CH₃C₆H₄ and 4-Cl-3-CH₃C₆H₃OCS₂)]. The compounds were characterised by elemental analyses, infrared, mass and heteronuclear NMR (¹H and ¹³C) spectroscopic studies. Thermogravimetric analysis and scanning electron microscopic analyses were also carried out for deeper investigation of the structural features. Comprehensive theoretical investigation was performed by applying density functional theory (DFT) calculations on vanadium and niobium complexes by the DFT/B3LYP/LANL2DZ method to obtain the optimised molecular geometry, vibrational frequencies, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), thermodynamic properties and various other quantum-mechanical parameters.     

Investigation of evolution hydrocarbon species on a Si surface during methane plasma with and without substrate bias, using infrared spectroscopy in multiple internal reflection geometry

We investigated evolution of hydrocarbon species on a Si surface during methane plasma both with and without substrate bias, using infrared spectroscopy in multiple internal reflection geometry (MIR-IRAS). We found that the relative density of the sp³-CH or sp³-CH₂ species to the sp³-CH₃ species was low in the low exposure regions, but that the relative density of the sp³-CH or sp³-CH₂ species increased as the exposure was higher. Substrate temperatures rose as the plasma exposure was higher. The changes of ratios would be ascribed to the substrate heating effect by plasma exposure, which would enhance the etching and/or hydrogen abstraction effects. We also found the change of CH_1-2/CH₃ ratios was enhanced when the high substrate bias was applied. The enhancement of the ratio was due to ion effects.     

Selective desorption from the binary coadsorbate C2H6CH3FNaCl by resonant vibrational excitation with laser infrared radiation

After measuring the linear infrared absorption spectrum of the coadsorbate, selective desorption of CH₃F from the binary coadsorbate C₂H₆CH₃FNaCl under ultrahigh vacuum conditions at 12o K stimulated by resonant CO₂ laser pulses of small fluence ～ 0.1 J·cm^t?2 has been carried out. No desorption of ethane, which is slightly more volatile, but has no significant infrared absorption at the laser frequency, was observed. The primary activation step is the resonant multiphoton excitation of the most intense internal CH₃FNaCl adsorbate vibration, the CF stretching mode ν₃. The substance separation seems to indicate high localisation of the activation in this desorption and could be of interest for applications.     

Cross relaxation in the rotational inversion doublets of ammonia in the far infrared

The effect of cross relaxation due to inelastic collisions on the inversion doublets of ammonia in the far infrared was studied by interferometric spectroscopy. Line widths and cross-relaxation rates were measured for several rotational transitions, using CH₂ = CF₂, C₂H₆, CF₄ and SF₆ as perturbing gases in the pressure range from 1 to 17.5 atm. The J-dependence of the observed cross-relaxation rates was calculated using a first Born approximation.     

CO2 and C2H4 grafting to the native defects of ion-bombarded porous silica

• )₄, though it is expected to relax via formation of peroxidic bridges), and the oxygen-bridge vacancy (which in the absence of relaxation can be described as a diradical center (≡Si^•)₂– the E^′′ center). These radicals react with the residual atmosphere according to completely new pathways: the bombardment in a CO₂ atmosphere results in the formation of ester-like and carboxylate groups, stable up to 500 °C at least, inserted in the SiO₂ network at the oxygen-bridge vacancies. The bombardment in a C₂H₄ atmosphere results in more complex configurations: the oxygen-bridge vacancy reacts at room temperature with ethylene forming a Lewis adduct which, after heating at 500 °C, presumably reverts to a -CH₂-CH₂- bridge in between silicon atoms; the silicon-link vacancy likely reacts with C₂H₄ forming CH₃CHO. These conclusions, based on experimental data (mainly infrared spectroscopy), are also supported by extended quantum mechanical calculations (density-functional methods and ab initio molecular dynamics). Received: 6 March 1998/Accepted: 21 September 1998     

Absorption coefficients for hydrogen—III. calculated pressure-induced H2-H vibrational absorption in the fundamental region

The coefficient for absorption during H₂-H collisions was calculated for temperatures from 2000 to 7000 K and wave numbers between 100 and 40 000 cm^-1 for LTE. Because only transitions with Δν = 1 were considered, the absorption was near the fundamental at 4161 cm^-1 in the infrared. The model included mechanical anharmonicity, vibration-rotation interaction, excited vibrational states, and transverse components of the dipole moment. At 5500 cm^-1, 3750° K, and 1 atm pressure, inclusion of H₂-H vibrational absorption increased the absorption of pure hydrogen gas 48 per cent. An approximate formula for the H²-H absorption coefficient is given for rapid calculation.     

Stark spectroscopy with the CO laser: The ν3 fundamental band of H2CO

The ν₃ fundamental band of H₂CO (CH₂ scissoring motion) has been studied by means of CO laser Stark spectroscopy and conventional infrared absorption spectroscopy. The primary aim of the work was to determine the dipole moment of H₂CO in the v₃ = 1 state, and the value determined was 2.3250 ± 0.0025 D. The spectrum was analyzed with the inclusion of the Coriolis interactions among ν₃, ν₄, and ν₆ so that “true” rotational constants were determined for ν₃; “effective” constants obtained by ignoring these interactions were also determined. The ν₃ band origin was determined to be 1500.174 ± 0.002 cm^?1. The H₂CO spectrum was also used as a means of determining the frequencies of some ¹³C¹⁶O and ¹²C¹⁸O laser lines in the 1500 cm^?1 region relative to ¹²C¹⁶O lines.     

Thermal reactions of 2-iodoethanol on Cu(1 0 0)

Temperature-programmed reaction/desorption, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy have been employed to investigate the reactions of ICH₂CH₂OH on Cu(1 0 0) under ultrahigh-vacuum conditions. ICH₂CH₂OH can dissociate on Cu(1 0 0) at 100 K, forming a -CH₂CH₂OH surface intermediate. Density functional theory calculations predict that the -CH₂CH₂OH is most probably adsorbed on atop site. -CH₂CH₂OH on Cu(1 0 0) further decomposes to yield C₂H₄ below 270 K. No evidence shows the formation of -CH₂CH₂O- intermediate in the reactions of ICH₂CH₂OH on Cu(1 0 0) in contrast to the decomposition of BrCH₂CH₂OH on Cu(1 0 0) and ICH₂CH₂OH on Ag(1 1 1) and Ag(1 1 0), exhibiting the effects of carbon-halogen bonds and metal surfaces.     

Kinetic study on effect of novel cationic dimeric surfactants for the cleavage of carboxylate ester

Kinetic study has been performed to understand the reactivity of novel cationic gemini surfactants viz. alkanediyl‐α,ω‐bis(hydroxyethylmethylhexadecylammonium bromide) C₁₆‐s‐C₁₆ MEA, 2Br^? (where s = 4, 6) in the cleavage of p‐nitrophenyl benzoate (PNPB). Novel cationic gemini C₁₆‐s‐C₁₆ MEA, 2Br^? surfactants are efficient in promoting PNPB cleavage in presence of butane 2,3‐dione monoximate and N‐phenylbenzohydroxamate ions. Model calculation revealed that the higher catalytic effect of ethanol moiety of gemini surfactants (C₁₆H₃₃N⁺ C₂H₄OH CH₃ (CH₂)_S N⁺ C₂H₄OH CH₃C₁₆H₃₃, 2Br^?, s = 4, 6) is due to their higher binding capacity toward substrate. This is in line with finding that binding constants for novel series of cationic gemini surfactants are higher than conventional cationic gemini (C₁₆H₃₃N⁺(CH₃)₂(CH₂)_SN⁺(CH₃)₂C₁₆H₃₃, 2Br^?, s = 10, 12), cetyldimethylethanolammonium bromide and zwitterionic surfactants, i.e. C_nH_2n+1N⁺Me₂ (CH₂)₃ SO₃^? (n = 10; SB3‐10). The fitting of kinetic data was analyzed by the pseudophase model. Copyright © 2013 John Wiley & Sons, Ltd.     

Concentration Fluorescence Quenching of L(-)-Tyrosine in Aqueous and Nonaqueous Solutions

Abstract

A number of studies have demonstrated the dependence of both the fluorescence lifetimes and quantum yields of tyrosine in solution upon the nature of the solvent as well as upon the absence or the presence of air in the tyrosine solutions employed. Photobleaching of tyrosine in vacuum at pH 6.1 was found to be practically zero, whereas exposure of tyrosine to the full light of a Hglamp for 10 to 20 minutes gave rise to formation of non-fluorescing photoproducts⁽¹⁾. In addition, the phosphorescence lifetimes of tyrosine were determined as 2.7⁺?0.2 sect 2.7⁺0.2 sec. and < 1 sec in 1% ETOH in aqueous solution and at pH 6.1 and pH 13, respectively(l). The very long phosphorescence lifetimes are definitely responsible to a considerable extent as far as photobleaching is concerned. However, the participation of the excited singlet state cannot be ruled out. In a review, the fluorescence lifetimes of tyrosine in queous solutions were found to vary between 2.6 nsec to 3.6 nsec⁽²⁾. On the other hand, the fluorescence quantum yields of tyrosine and various anologous compounds displayed a strong dependence upon the solvent. Such solvents used were water, n-butanol and p-dioxane. The following values of φ_fl were obtained: For p-HO-C₆H₄ -CH₂COOH; φ_fl=0.01, 0.22 and 0.34; for p-HO-C₆H₄-CH₃; φ_fl= 0.23, 0.39 and 0.45 and for p-HO-C₆H₄-CH₂CN; φ_fl =0.16, 0.34 and 0.34, respectively⁽³⁾. Furthermore, the value φ_fl of p-HO-C₆H₄-CH₂CH(NH⁺ ₃)C00^? in aqueous solutions was found to be 0.21, where- as that of p-HO-C₆H₄-CH²CH(NH⁺ ₃)COOH in similar solutions was 0.06. The fluorescence lifetime and quantum yield of phenol in Ethanol were found to be 4.7 nsec and 0.10, respectively⁽⁴⁾.     

Diode laser measurements of temperature-dependent collisional-narrowing and broadening parameters of Ar-perturbed H2O transitions at 1391.7 and 1397.8 nm

High-resolution absorption lineshapes of two H₂O transitions near 7185.60 and 7154.35 cm⁻¹ have been recorded in a heated static cell as a function of temperature (296-1100 K) and pressure (6-830 Torr) using two distributed-feedback diode lasers. The measured absorption spectra are least squares fit to both Voigt and Galatry profiles. Strong collisional-narrowing effects are observed in the Ar-broadened H₂O spectra at near-atmospheric pressure due to the relatively weak collisional broadening induced by Ar-H₂O collisions, while collisional narrowing is not significant for pure H₂O absorption lineshapes. Line strengths and self-broadening coefficients are inferred from the pure H₂O absorption spectra and compared with published data. Temperature dependences of the Ar-induced broadening, narrowing, and shift coefficients are determined using Galatry fits to the absorption data. The measured collisional-narrowing parameters have similar temperature dependence to the collisional-broadening coefficients.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Infrared spectroscopic study of thermal annealing effects of hydrocarbon species on a Si surface exposed to methane plasma

We have investigated the thermal annealing effects of hydrocarbon species on the methane-plasma exposed silicon surface, investigated by in situ infrared absorption spectroscopy (IRAS) in multiple internal reflection (MIR) geometry. The proportion of types of hydrocarbon species is not remarkably changed in the hydrocarbon network that consists of sp-, sp²- and sp³-CH_X species by annealing at moderate temperatures. On the other hands, the proportion is drastically changed in the network that is mainly composed of sp³-CH_X species by annealing at moderate temperatures. It suggests that excess CH₃ species in the film is not stable against thermal annealing and would be converted to sp³-CH_1-2 species by annealing at moderate temperatures. And the data also show that sp²-CH species is more stable against the thermal annealing than sp³-hydrocarbon species.