Low temperature laser fluorescence and excitation spectra of free base phthalocyanine in normal alkanes matrices (Shpolskii effect)

Excitation and fluorescence spectra of free base phthalocyanine were studied in matrices of normal alkanes (C₈H₁₈, C₁₂H₂₆, C₁₆H₃₄) at low temperatures (5 to 30 K). Narrow band excitation of fluorescence using a pulsed tunable dye laser was used for site selection to eliminate ambiguities due to impurities and multiple sites. Fluorescence and excitation spectra show quasiline structure. Multiplicity of 0-0 transitions depends on the chain length of normal alkanes. The spectra and frequencies of normal vibrations are compared with those of phthalocyanine in other n-alkanes (C₉H₂₀, C₁₀H₂₂) and noble gas matrices (Ar, Ne) under different excitation conditions.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

A study of molecular reorientation in a series of liquid n-alkanes using light-scattering spectroscopy

The spectra of the depolarized (VH) light scattered from the n-alkanes C₆H₁₄, C₈H₁₈, C₁₀H₂₂, C₁₂H₂₆, C₁₄H₃₀, C₁₅H₃₂ and C₁₆H₃₄ have been measured using a high resolution piezo-electrically scanned Fabry-Perot interferometer. The values of the molecular relaxation times τ _s derived from the spectra are compared with relaxation times τ _f derived from flow birefringence. The experimental results are discussed in terms of a phenomenological activation energy and also in terms of the coupling between the molecular reorientation and the hydrodynamic shear modes, allowing estimates of the strength of the coupling between these modes to be made.     

Auger spectroscopy of polyethylene and poly (ethylene oxide)

The X-ray excited Auger spectra of polyethylene and poly(ethylene oxide) have been corrected for Auger electron energy losses due to interactions with the solid and compared to the corresponding spectra of gas phase molecular analogs. The corrected polyethylene spectrum is an extrapolation of trends observed in the spectra of gas phase alkanes from CH₄ through C₆H₁₄. The O(KVV) spectrum of poly(ethylene oxide) is similar to that of methyl ether, consistent with similar nearest neighbor environments for the oxygen atoms in the two materials. In contrast, the C(KVV) spectrum of poly(ethylene oxide), a material which contains C-C bonds, is better approximated by the spectrum of ethane (H₃C-CH₃). A comparison of the polyethylene Auger spectrum with the spectra of the normal alkanes and with a self-fold of its X-ray excited valence band photoemission (single hole) spectrum indicates the presence of correlated two-hole final states in the case of polyethylene.     

Theory of two-phonon absorption processes in liquid paraffins

Calculated absorption spectra are given for linear C₈H₁₈, C₁₀H₂₂, C₁₆H₃₄ and C₂₀H₄₂ chains, based on the assumption of a two-phonon absorption mechanism. In the present work the normal modes of vibration of different finite chains are computed directly, without recourse to the Pitzer sampling approximation and without the assumption of strict k-selection rules. The calculated spectra are found to be much more sensitive to chain length than the experimental spectra. A possible explanation of the relative insensitivity of the observed spectra is suggested in terms of a characteristic chain segment length common to all the chains. Ironically, the apparent importance of chain segmentation in the two-phonon absorption suggests that one-phonon transitions may also play a significant rôle in the absorption process.     

Force field calculation for inplane vibrations of ethylene usingcndo/Force method

cndo/Force method is used to evaluate redundancy-free internal valence force field (rfivff) for inplane vibrations of ethylene. The bending force constants, the stretch-band and bend-bend interaction force constants are predicted reasonably well in magnitude and sign by this method; whereas stretching force constants and stretch-stretch interactions are overestimated. Initial force field is set up by transferring stretching force constants from structurally-related molecules and including the rest of the force constants fromcndo force field. The field so constructed is subjected to refinement by the least square method. A total of 64 vibrational frequencies of C₂H₄, C₂D₄, C₂H₂D₂ and their¹³C isotopic modifications are used to determine force field containing 15 parameters. The final force field is found to be reasonable on the basis of frequency fits, potential energy distribution and band assignments.     

Carbon K-shell excitation of C2H2, C2H4, C2H6 and C6H6 by 2.5 keV electron impact

Energy loss spectra of 2.5 keV electrons in the region of the carbon K-edge in C₂H₂, C₂H₄, C₂H₆ and C₆H₆ are report     

Inelastic atom scattering from layers of atoms and molecules on Cu(110)

The vibrational properties of adsorbed layers have been studied using inelastic He atom scattering. The substrate was Cu(110) viewed along the [001] and [11̄0] azimuth. The adsorbates included, Kr, Xe, CH₄, CD₄, C₂H₆, CO, CO₂ and O₂ and covered the region of both physisorption and chemisorption. Despite a range of binding energies and mass ratios the vibrational frequencies showed no dependence on the momentum change, i.e. scattering was dispersionless, although intensity changes occurred in the inelastic peaks. There seemed to be no dependence of the adsorbate spectra on coverage below a monolayer. The peaks of CH₄ and C₂H₆ appeared broader than those of Kr and Xe suggesting molecular motions. Further, CH₄ and C₂H₆ gave very similar spectra. Both energy gain and loss events were observed in the inelastic spectrum. For those adsorbates which gave multilayer adsorption (Xe, C₂H₆) changes in the spectra were observed as the second layer developed. In the latter category also, mixed layers (Xe on C₂H₆, Xe on CO and C₂H₆ on Xe) were studied.     

Measurement of C2 and CH temperatures in argon‐acetylene low‐pressure microwave‐induced plasma

The emission spectra of C₂(d³Π_g–a³Π_u), CH(A²Δ–X²Π), and CH(B²Σ–X²Π) bands are analysed to measure rotational T_rot, vibrational T_vib, and gas temperature T_g from Ar/C₂H₂ (5–20% C₂H₂) microwave‐induced plasma (MIP). In case when helium and hydrogen are used in the gas mixture instead of argon, no significant change in T_rot is noticed. Both studied temperatures are insensitive in terms of the C₂H₂ percentage. From CH(0–0, A²Δ–X²Π) band R₂ branch lines, two T_rot (T_rot ～ 520–580 K for J′ = 3–9 and T_rot ～ 1,700–1,800 K for J′ = 10–17) are determined. The lower T_rot equals the T_g (500–700 K) measured from C₂ bands in this study. The H₂ Fulcher‐α diagonal bands are recorded as well in the H₂/C₂H₂ mixtures and T_rot～750–900 K of the H₂ ground state measured. T_vib ～ 6,000 K in Ar/C₂H₂ MIP is calculated from the integral intensity ratio of C₂(2,1) and C₂(3,2) bands.     

Photoelectron spectroscopy of some thiocyanates,isocyanates and isothiocyanates

Photoelectron spectra of some thiocyanates (RSCN, R = CH₃, C₂H₅, n-C₄H₉), isocyanates (RNCO, R = C₂H₅, n-C₄H₉) and isothiocyanates (RNCS, R = C₂H₅, n-C₄H₉) have been measured, to study interactions between nonbonding and π orbitals, mainly localized on the SCN, NCO or NCS fragments. The spectral interpretation of CH₃SCN is based on semiempirical CNDO/S calculations, sum-rule considerations, and intensity differences between He(I) and HE(II) spectra. For the larger molecules, comparison of the spectra is used as an aid in the interpretation. In a number of aromatic isocyanates (o?, m?, p-tolylisocyanate and m?, p-chlorophenylisocyanate), interactions between the isocyanate group and the highest occupied π and σ orbitals of the phenyl ring are studied. Spectra are assigned on the basis of semiempirical INDO/S calculations.     

Oxygen as promoter or poison in the catalytic dissociation of H2, C2H4, C2H2, and NH3 on Palladium

The dissociation rates of H₂, C₂H₄, C₂H₄, and NH₃ have been studied on oxygen covered Pd surfaces by measuring the water desorption rates during exposure to each of the molecules. These results are correlated with the hydrogen response of a Pd-MOS structure. The measurements show a trend (at 473 K) where oxygen blocks H₂ dissociation, blocks C₂H₄ dissociation only above a certain oxygen coverage, has no influence on C₂H₂ dissociation, and promotes NH₃ dissociation.     

Femto-Fourier transform-cavity enhanced absorption spectroscopy in a supersonic expansion

Proofs of principle spectra of C₂H₄, N₂O and C₂H₂, including H¹²C¹³CH in natural abundance, are reported, recorded in the 1.6?µm range in an Ar supersonic expansion using femto-Fourier transform–cavity enhanced absorption spectroscopy. The effective absorption pathlength in the jet-cooled sample is up to 78?m and the optimal S/N is over 2300. The data processing is detailed. Saturation effects are reported for the C₂H₂ bands.     

Dissociative photoionization of l-menthone: An experimental and theoretical study

The dissociative photoionization mechanism of l-menthone has been investigated with photoionization mass spectrometry using synchrotron radiation. The adiabatic ionization energy (IE) of l-menthone and the appearance energies (AE) of its major fragment ions C₉H₁₅O⁺, C₉H₁₇⁺, C₈H₁₆⁺, C₇H₁₁O⁺, C₆H₁₀O⁺, C₆H₉O⁺, C₅H₈O⁺, C₅H₁₀⁺, C₄H₆O⁺, C₅H₉⁺, C₄H₈⁺, C₄H₇⁺, C₃H₇⁺, C₃H₆⁺, C₂H₂O⁺, and CH₃⁺ are determined with their photoionization efficiency (PIE) spectra in the photon energy region of ∼8−15.5 eV. Breakdown diagrams identifying the major products are presented. Dissociative photoionization channels for formation of these fragment ions are proposed based on comparison of determined experimental appearance energies and energies predicted with the DFT calculations. According to our results, the experimental dissociation energies are in fair agreement with the theoretical values of the possible photodissociation channels of C₁₀H₁₈O.     

Molecular dynamics simulation for sodium atom in and on the two layers of C150H 30 graphite plane

For inspection of thermal behaviors of sodium (Na) atom in the bulk and on the surface of two layered hydrogen terminated cluster model, 2C₁₅₀H₃₀, the molecular dynamics calculation was taken place at molecular mechanics 2 level. From the requirement of structural optimization, interlayer distance of 2C₁₅₀H₃₀ is 3.38 Å which is consistent with the observed value. In the cluster models intercalated and adsorbed by one Na atom, C₁₅₀H₃₀·Na·C₁₅₀H₃₀ and Na·2C₁₅₀H₃₀, respectively, the Na atom is stabilized beneath and above the nearest central carbon atom, C₀, in the upper layer where the distances, Na-C₀, are 2.76 and 3.16 Å, respectively. Adsorption of the Na atom to the surface has no influence on the geometrical structure of cluster model, whereas, intercalation to two layers expands the interlayer distance maximally to 5.01 Å which will be responsible for the carbon expansion of graphite electrode in cryolite melt-alumina slurries. Diffusion processes are observed above 200 K for the Na atoms stabilized in both sites. Although the Na atom migrates parallel to the layers in the range between 200 and 300 K in C₁₅₀H₃₀·Na·C₁₅₀H₃₀, it moves above the carbon layer from the center to the circumference periodically below 250 K and gets out at 300 K for Na·2C₁₅₀H₃₀. The migration rates of Na atom are almost the same irrespective of the diffusion areas.     

Review of quantitative spectroscopy of polyynes

We propose a review of quantitative spectroscopy of polyynes in the infrared and ultraviolet domain focusing on essential spectroscopic parameters for the interpretation of observed spectra in the infrared and ultraviolet domain and for photochemical modeling. We point at the lacking data in both wavelength domains for C₂H₂, C₄H₂, C₆H₂, C₈H₂ and propose downloadable files of the ultraviolet absorption coefficient ready to use for photolysis rate calculations. For longer polyynes, we calculate extrapolated ultraviolet spectra and calculate their photolysis rate. Using a simplified photochemical model of the polyynes in Titan and CRL618, we predict their relative abundance and compare them with the observed ones. This also leads us to predict the abundances of the longer polyynes.     

Infrared crystal spectra of C2H4, C2D4, and as-C2H2D2 and the general harmonic force field of ethylene

Carbon-13 frequency shifts for C₂H₄, C₂D₄, and as-C₂H₂D₂ have been measured in isotopic solid solutions in crystalline films at 60 K. All but two of the shifts (for as-C₂H₂D₂) are compatible with recently determined ζ data for C₂H₄, with ¹³C frequency shifts for C₂H₄ and C₂D₄ in the gas phase and with conventional frequency data. Together, these data completely determine with precision all 18 parameters of the GHFF for ethylene, the previous ambiguity in choice between two sets of A_g species force constants being removed. The force field reproduces closely the observed centrifugal distortion constants for C₂H₄, a ζ constant observed for trans-C₂H₂D₂, and the inertia defects for C₂H₄, C₂D₄, and as-C₂H₂D₂. Vibration and rotation constants for all isotopically deuterated ethylenes are calculated.Possible explanations for the two anomalous crystal shifts in as-C₂H₂D₂ involve the effects of the crystal field, and failure of the use of Dennison's rule for making anharmonic corrections to the shifts. The former explanation is preferred as a result of thorough analysis of the anharmonicity constants for as-C₂H₂D₂ determined from many overtone and combination bands in the gas and crystal spectra.     

Vibrational spectra of styrene-H8, -D3, -D5, and -D8

Infrared and Raman spectra of C₆H₅CHCH₂, C₆H₅CDCD₂, C₆D₅CHCH₂, and C₆D₅CDCD₂ liquids are analyzed to assign their fundamental vibrations.     

Elektronenspinresonanz vonU 2-Folgezentren in Alkalihalogenid-Kristallen

UV-irradiation at low temperatures may bring hydrogen atoms into interstitial sites (produceU ₂ centers) in alkali halides. At about 100 °K the hydrogen atoms begin to leave their sites and may react with any diamagnetic centerX to a paramagnetic center HX. In this paper CN^? and NCO^? ions are used for X. The paramagnetic centers are investigated by the method of ESR. The spectra and thermal properties of¹H¹²C¹⁴N^?,²H¹²C¹⁴N^?,¹H¹³C¹⁴N^?,¹HNCO^? and²HNCO^? are described. As well signals are found, which may be attributed to the²H¹³C¹⁴N^? center. A simple cryostat is described for use at temperatures continously variable between 25 °K and 500 °K.     

Evaluation of jet-cooled laser spectroscopy for simplifying infrared spectra

The effect of jet cooling on the vibration-rotation spectra of several polyatomic molecules has been investigated using diode-laser absorption spectroscopy. Vibration-rotation spectra in jet expansions is considered in terms of several factors including rotational and vibrational distributions, line strengths and the rotational structure of individual bands. The diode-laser spectra of PF₃, CF₃Cl, C₃H₆, C₂H₃F, and CH₃CCH recorded in a molecular beam are examined with the above criteria.     

A photoelectron spectroscopic study of the carburization of MoO3

MoO₃ and Mo samples containing copper were treated with different hydrocarbon/hydrogen gas mixtures. The formation of Mo₂C was followed by X-ray photoelectron spectroscopy (XPS). Spectra taken in the Mo 3d, C 1s, O 1s, Cu 2p and Cu KLL regions demonstrated that the treatment with the hydrocarbon/hydrogen gas mixtures led to the formation of Mo₂C. From the comparison of the effects of various hydrocarbons on the XP spectra of Mo 3d we can state that the reduction of MoO₃ starts at the lowest temperature for C₂H₆/H₂ (600 K) followed by CH₄/H₂ (700 K) and C₄H₁₀/H₂ (723 K). Binding energies of Mo 3d_5/2 characteristic for Mo₂C are measured in the range of 227.7-228.0 eV. These values were attained at 900 K for CH₄/H₂, at 800 K for C₂H₆/H₂ and at 873 K for C₄H₁₀/H₂. Addition of copper to MoO₃ catalyzed its reduction and promoted the carburization process.