Metastable transitions in the mass spectra of fluoro-ethylenes

Metastable transitions in the mass spectra of six fluoroethylenes are reported. In several cases in which HF is the neutral species lost, 0.4 to 0.7 eV of kinetic energy is liberated. In two fragmentations, it is shown that the kinetic energy release is only about half the minimum energy of activation of the back reaction calculated from thermochemical data. Evidence is presented to support the view that in some cases at least, fragmentation occurs from two or more electronic states of the molecular ion.     

Metastable transitions in the mass spectra of methyl and phenylthiohydantoin derivatives of amino acids

The mass spectra of a number of methyl- and phenylthiohydantoin amino acid derivatives have been obtained. The major metastable transitions occurring in the mass spectra of these derivatives have been identified and measured. The major fragmentation pathways associated with the metastable transitions have been outlined and are discussed for each group of compounds. Inspection of the metastable data has shown that there is at least one unique metastable transition occurring for each thiohydantoin derivative which may be used to uniquely identify that derivative in the presence of a mixture of thiohydantoin derivatives obtained from the Edman degradation of a peptide or protein. The use of metastable ions to uniquely identify thiohydantoin derivatives in mixtures has proven useful in the identification of the MTH and PTH derivatives of glycine whose molecular ions are not unique and for resolving such ambiguities as occur for example in the mixture of leucine and isoleucine.     

Metastable transitions in the mass spectra of ketals and ketones. Competition between loss of small and large radicals

An investigation of competing metastable transitions in the mass spectra of ethylene ketals R_SR_LC(OCH₂)₂ (where R_L is a larger n-alkyl group than R_S) has established that in most cases R_S is lost with a lower activation energy than R_L. This technique has also been applied to ketones R_SR_LC?O, to show again that R_S is usually lost with the lower activation energy (thus supporting earlier data based on relative daughter ion abundances at the threshold). In the classes of compounds so far investigated, although [M⁺ ? R_S] ions are formed with lower activation energies than [M⁺ ? R_L] ions, the ion yield of [M⁺ ? R_S] ions is anomalously low from ions of high internal energy. Factors which may influence the [M⁺ ? R_S]/[M⁺ ? R_L] ratio of daughter ion intensities are examined. It is suggested that at the threshold [M⁺ ? R_S] and [M⁺ ? R_L] ions may be formed with rearrangement, or from an electronic state that cannot be effectively populated from molecular ions of high internal energies.     

Metastable mesophases

Mesophases are briefly summarized and defined on a uniform basis, making use of order and mobility parameters. A schematic one-component phase diagram is then reviewed that includes equilibrium as well as nonequilibrium phases. Assuming only five condensed phases (crystal, melt, glass, mesophase, and mesophase glass), fifteen different phase areas exist with simultaneous presence of up to three phases. Examples of all phase areas are documented with results from our laboratory. This scheme can be extended to more components and more than these five phases and produces then many more possible phase areas than can be handled experimentally at the present.     

Metastable Dianions and Dications

A theoretical study of metastable dianions and dications has been carried out at the CCSD(T)//MP2 level. MX₃²⁻ and LX₄²⁻ (M=Li and Na, L=Be and Mg, X=F and Cl) have been considered as dianions, M₃X²⁺ (M=Li and Na, X=F and Cl), YH₃²⁺ and ZH₄²⁺ (Y=F and Cl and Z=O, S) as dications. Minima structures are found in all cases, but they are less stable than the corresponding dissociated pair of mono-ions. The dissociation profile of the molecules in two mono-ions has been explored showing in all cases a maximum that prevent their spontaneous dissociation. The strength and nature of the chemical bond in the dianions and dications have been analyzed with the QTAIM, NBO and LMOEDA method and compared to the corresponding monoanions and monocations.     

Analysis of polymers by mass spectrometry: Metastable mapping of transitions from pyrolysis products of an aromatic polyamide

Metastable mapping was applied to the analysis of the mixture of the pyrolysis products obtained from an aromatic polyamide, pyrolysed directly in a mass spectrometer. This technique permits a rapid analysis of the components and provides a method for assigning structures through the study of molecular ions, characteristic fragmentations and comparisons of daughter and parent ions of authentic samples. Collisionally activated decomposition spectra were always obtained in order to induce a higher intensity in the metastable transition. The thermal decomposition mechanism of the aromatic polyamide investigated here occurs via an intramolecular exchange and a concomitant N-H hydrogen transfer process with the formation of compounds with amine and/or succinimide end-groups.     

Conversion of n-butane on H-mordenite catalysts

Conversion of n-butane on various mordenite catalysts have been studied at temperatures ranging within 150–500°C. The isomerization activity of the catalysts is shown to depend on the temperature, mordenite composition and its molar ratio of SiO₂/Al₂O₃.

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150–500°C - H-, . , , SiO₂/Al₂O₃.

     

Metastable ions in chemical ionization

The ion [C₃H₅]⁺ generated in a chemical ionization source by a variety of methods, including protonation and charge exchange, exhibits a metastable peak for H₂ loss which is two orders of magnitude weaker than that formed in an electron impact source. The stable [C₃H₅]⁺ ions generated by electron impact and chemical ionization undergo collision-induced dissociation to a comparable extent, both losing H₂ by only one of the two competitive mechanisms observed for metastable ions. In contrast to the behavior of [C₃H₅]⁺, the molecular ions of p-substituted nitrobenzene, generated by charge exchange at high source pressure, yield composite metastable peaks for NO loss which are very similar in shape and intensity to those generated by electron impact. The contrasting behavior of the metastable ions extracted from high pressure ion sources in the two systems may be due to differences in the efficiencies of quenching of the ionic states responsible for fragmentation as metastable ions. It is noteworthy that the NO loss reactions require considerably lower activation energies than does the H₂ loss reaction.     

Hyperfine structure and Zeeman effect studies in the 6p7p-6p7s transitions in Bi II

The hfs and hfs Zeeman splitting of nine lines from the array 6p7p→6p7s as well as lines λ = 496.9 nm (6p8p ³D₂→6p7s ³P₂) and λ=581.8 nm (6p8s ³P₀→6p7p ³D₁) of Bi II have been analysed. The Zeeman effect studies were performed for transverse direction of observation and separated π; and σ components of lines. The electrodeless discharge tube containing metallic Bi was used as the light source. The spectral apparatus consisted of a sliver-coated Fabry-Perot etalon and a grating spectrograph combined with a diode array detector. In the analysis of the spectra we used the computer simulation technique. The magnetic-dipole (A) and the electric-quadruple (B) hfs constants as well as Lande-g_j factors for the level 6p8p ³D₂ and all levels of configurations 6p7s and 6p7p (with the exception of 6p7p ³S₁) were determined. Our results are compared with recent theory and other experiments.     

Far infrared spectrum and conformational potential function of n-butane

The far i.r. spectrum of gaseous n-butane obtained at 0.06 cm⁻¹ resolution is reported between 80 and 230 cm⁻¹. Several transitions for the asymmetric torsion of the trans conformer have been identified. Utilizing these data along with the previously reported asymmetric torsional transitions of the gauche conformer from Raman spectroscopic data, the potential function for the conformational change has been obtained. The determined potential parameters were found to be: V₁ = 181, V₂ = 148, V₃ = 1154 and V₆ = −33 cm⁻¹. The s-trans to gauche, gauche to gauche, and gauche to s-trans barriers in cm⁻¹ were found to be: 1315 (3.76 kcal/mol), 1090 (3.12 kcal/mol) and 1070 (3.06 kcal/mol), respectively. The potential functions obtained from these spectroscopic data are consistent with the trans to gauche energy difference, but not with the high trans/cis potential barrier suggested by recent ab initio calculations.     

Oxidative activation of n-butane on sulfated zirconia

Catalytic activation and conversion of light alkanes by sulfated zirconia is unequivocally shown to be initiated by producing small concentrations of olefins. This occurs via stoichiometric oxidative dehydrogenation of butane by SO3 or pyrosulfate groups to butene (present mostly as alkoxy groups), water, and SO2. Thermal desorption and in situ IR spectroscopy have been used to determine all three reaction products. The concentration of butene formed determines both the catalytic activity of sulfated zirconia as well as the deactivation via formation of oligomers. The thermodynamics of the oxidative dehydrogenation of n-butane by different SZ surface structures has been examined by density functional (DFT) calculations. The calculations show that pyrosulfate or re-adsorbed SO3 species have the highest oxidizing ability.     

Conjugate conversion of methanol and n-butane on zinc-zirconium catalysts

Conversion of n-butane, methanol, and their mixture on ZSM-5 zeolite catalysts containing zinc and/or zirconium was studied, and ways were found to control the yield and ratio of major reaction products: C₁-C₃ alkanes, C₂-C₄ alkenes, C₅-C₇ isoalkanes, and arenes. The schemes of formation of these products were suggested.     

Metastable effects onmartensitic transformation in SMA

The behavior of shape memory alloys (SMA) allows their use as a passive smart material. In particular, the existence of a hysteretic cycle in the domain of the elementary coordinates strain-stress-temperature (σ, ε, T) suggests its application for damping in mechanical and/or in civil engineering. We are working in the application of SMA as dampers for earthquakes in small houses as family homes. For dampers installed in the inner porticos of the house, the suggested SMA is the CuAlBe and, eventually, the NiTi. At room temperature the used SMA wires induces forces situated between 2–3kN/wire. The properties related with the damping applications for CuAlBe and NiTi, i.e., the SMA creep and the self-heating will be presented, together with some other minor stress and temperature effects on NiTi modifying the hysteretic behavior.     

Metastable peak study in methylactophenone isomers

The relative intensity of the metastable peaks at 70 eV appearing at m/z 105.7 and 69.6 in the mass spectra of methylacetophenone isomers, as well as the kinetic energy (T_1/2) released with the peaks at 14 and 70 eV respectively, are reported. The profile of all the metastable peaks studied has been found to be approximately flat-topped. For the same transition it is found that the kinetic energy released with the metastable peaks formed by unimolecular decomposition of the three isomers decreases from the ortho to the para isomer. In addition, the kinetic energy released during the same transition is found to be roughly directly proportional to their corresponding intensity ratios. This result, together with the observation that the energy released with each metastable peak decreases by lowering the electron energy, may reveal the role of the internal energy of the reacting ions in producing the kinetic energy associated with the metastable peaks produced from methylacetophenone isomers.     

Metastable ion fragmentation processes in n-alkanes

The n-alkanes, propane to heptane, have been studied in a modified MS-9 mass spectrometer under conditions that enabled the daughter ions, resulting from metastable fragmentation processes occurring in the first field free region, to be observed with high sensitivity. The precursor ions in these fragmentations have been identified unambiguously and a general fragmentation scheme for the n-alkanes is proposed. The mass spectrometer incorporated a variable width monitor slit and narrow settings of this slit improved the energy resolution so that fine structure could be observed in some of the ‘metastable peaks’. The implications of this fine structure are discussed.     

Solvothermal Route to Prepare the Metastable Phase 3c-Fe7S8 with Hexagonal Platelet Morphology

The metastable phase 3c-Fe7S8 with the hexagonal platelct morphology has been prepared by using solvothermal route.The product was characterized by mcans of X-ray powder diffraction(XRD) and transmission electron microscopy (TEM) and X-ray photoelectron speetra (XPS).The experiment results show that the as-prepared Fe7S8 is a metastable phase with the hexagonal platelet morphology.     

Non-resonant third-order susceptibilities measured for ethane,propane and n-butane

Third-order non-linear susceptibilities have been measured for ethane, propane and n-butane at three wavelengths in the visible region by means of gas-phase electric-field-induced second-harmonic generation (ESHG). The susceptibilities are found to be large and strongly frequency dependent. The possible application of these results to the calibration of the non-resonant background in coherent anti-Stokes Raman scattering (CARS) measurements is discussed.