Tims and maldi tof of endohedral metallofullerenes

Mass spectral studies (both TIMS – thermal ionization and MALDI TOF – matrix-assisted laser desorption time-of-flight mass spectrometry) of the endohedral metallofullerenes, Li@C60,Li2C70 and 99mTc@C70,provided detailed structural and reactivity information about these unusual species. MS experiment revealed that both fullerenes and endohedral metallofullerenes fragment by multiple C2 loss. However, a difference in the terminal fragmentation products was observed for metallofullerene relative to C60, suggesting that the encapsulation metal strongly impactsthe fragmentation product. Singly charged cations of the metallofullerenes (M@Cn + ) were completely unreactive in the gas phase with oxygenated compounds such as ethylene oxide: however, the corresponding neutral species appear to react readily with oxygenated species. Collisional dissociation of the ionized endohedral fullerenes listed above revealed multiple C2 loss (either as sequential C2 loss or larger C2n eliminations) to generate similar terminal fragmentation products, which might be predicted due to the similar ionic radii of the encapsulated metals. The observed ionization energies of endohedral molecules were 5.9 ± 0.1 eV, 5.3 ± 0.1 eV and 5.7 ± 0.1 eV, respectively.Physical chemistry 2004 : 7th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 21-23 September 200

Study of the vaporization of LiI, LiI/C-70, LiI/LiF/C-70 from a Knudsen cell located in the ionization chamber of a mass spectrometer

The vaporization of LiI, LiI/C-70 and LiI/LIF/C-70 was studied using a Knudsen cell located in the ionization chamber of a magnetic sector mass spectrometer in the temperature range from 350 degrees C to 850 degrees C. The ion species, LinI+ (n = 2, 3, 4 or 6) were identified from the mixture LiI/C-70, while the clusters LinI+ and LinF+ (n = 2, 3, 4, 5 or 6) were detected from a mixture LiI/LiF/C-70. The intensities of LinI+ were higher than the emission of LinF+ cluster when the ratio of LiI to LiF was 2:1. By contrast, the emission of LinF+ is favored when the ratio of LiI to LiF was 1:2. These results show that the vaporization of a mixture LiI/LIF/C-70 from a Knudsen cell located in the ionization chamber of a mass spectrometer represents an efficient and simple way to obtain and investigate clusters of the type LinX, X = F or I. In this work, it was also shown that the trends of the In (Intensity, arb. units) versus temperature for all LinI+ clusters below and above the melting point of LiI were not same. This suggested that the manner of formation of these clusters could be different due to changes in temperature

Tims and maldi tof of endohedral 99mTc@C60 metallofullerene

Mass spectral studies (both TIMS – thermal ionization and MALDI TOF – matrixassisted laser desorption time-of-flight mass spectrometry) of the endohedral metallofullerenes, 99mTc@C60 and 99mTc@C70, provided detailed structural and reactivity information about these unusual species. MS experiment revealed that both fullerenes and endohedral metallofullerenes fragment by multiple C2 loss. However, a difference in the terminal fragmentation products was observed for metallofullerene relative to C60, suggesting that the encapsulation metal strongly impacts the fragmentation product. Singly charged cations of the metallofullerenes (M@Cn + ) were completely unreactive in the gas phase with oxygenated compounds such as ethylene oxide: however, the corresponding neutral species appear to react readily with oxygenated species. Collisional dissociation of the ionized endohedral fullerenes listed above revealed multiple C2 loss (either as sequential C2 loss or larger C2n eliminations) to generate similar terminal fragmentation products, which might be predicted due to the similar ionic radii of the encapsulated metals. The observed ionization energies of endohedral molecules were, 5.1 ± 0.1 eV and 5.3 ± 0.1 eV, respectively.Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

A TPD-MS study of glassy carbon surfaces oxidized by CO2 and O-2

The temperature-programmed desorption (TPD) method combined with mass spectrometric (MS) analysis has been applied to investigate the surface properties of carbon materials. The apparatus consisting of a temperature-programmed furnace and a quadrupole Mass spectrometer was constructed in order to characterize the surface of differently treated glassy carbon samples. In this work, samples of glassy carbon exposed to air, CO2 and O-2 were examined. The desorption of H2O, CO and CO2, as major products, indicated the presence of different oxide groups. The amount of these groups for all samples was calculated. It is concluded that oxidation affects the nature and the amount of die surface oxide groups and contributes to their increased stability

Production of Heterogeneous Superalkali Clusters Linf (N=2-6) By Knudsen - Cell Mass Spectrometry

The superalkali clusters are important because they can be considered as potential building block for the assembly of novel nanostructured materials with unique structural, electronic, optical, magnetic, and thermodynamic properties. We have modified and used the Knudsen cell mass spectrometer in order to obtain and measurement of the ionization potentials of the superalkali clusters. In this work the clusters LinF (n = 2 - 6) have produces in the vapor over a mixture of lithium fluoride and lithium iodide by means of Knudsen cell which is placed into ionization chamber of the magnetic sector mass spectrometer. The simultaneous production and mass spectrometric detection of the ionic of clusters provide information on the conditions of formation and the distribution of these ion species. It is observed that the ions of clusters with an even numbered of lithium atoms are more stable than the ions of clusters with an odd numbered of lithium atoms. The clusters Li5F and Li6F were detected experimentally for the first time with their ionization energies of (4.29 +/- 0.25) eV, and (4.24 +/- 0.25) eV, respectively

Formation of positive cluster ions LinBr (n=2-7) and ionization energies studied by thermal ionization mass spectrometry

Clusters of the type LinX (X = halides) can be considered as potential building blocks of cluster-assembly materials. In this work, LinBr (n = 2-7) clusters were obtained by a thermal ionization source of modified design and selected by a magnetic sector mass spectrometer. Positive ions of the LinBr (n = 4-7) cluster were detected for the first time. The order of ion intensities was Li2Br+ Li4Br+ GT Li5Br+ GT Li6Br+ GT Li3Br+. The ionization energies (IEs) were measured and found to be 3.95 +/- 0.20 eV for Li2Br, 3.92 +/- 0.20 eV for Li3Br, 3.93 +/- 0.20 eV for Li4Br, 4.08 +/- 0.20 eV for Li5Br, 4.14 +/- 0.20 eV for Li6Br and 4.19 +/- 0.20 eV for Li7Br. All of these clusters have a much lower ionization potential than that of the lithium atom, so they belong to the superalkali class. The IEs of LinBr (n = 2-4) are slightly lower than those in the corresponding small Li-n or LinH clusters, whereas the IEs of LinBr are very similar to those of Li-n or LinH for n = 5 and 6. The thermal ionization source of modified design is an important means for simultaneously obtaining and measuring the IEs of LinBr (n = 2-7) clusters (because their ions are thermodynamically stable with respect to the loss of lithium atoms in the gas phase) and increasingly contributes toward the development of clusters for practical applications. Copyright (C) 2012 John Wiley and Sons, Ltd

Production of Heterogeneous Superalkali Clusters Linf (N=2-6) By Knudsen - Cell Mass Spectrometry

The superalkali clusters are important because they can be considered as potential building block for the assembly of novel nanostructured materials with unique structural, electronic, optical, magnetic, and thermodynamic properties. We have modified and used the Knudsen cell mass spectrometer in order to obtain and measurement of the ionization potentials of the superalkali clusters. In this work the clusters LinF (n = 2 - 6) have produces in the vapor over a mixture of lithium fluoride and lithium iodide by means of Knudsen cell which is placed into ionization chamber of the magnetic sector mass spectrometer. The simultaneous production and mass spectrometric detection of the ionic of clusters provide information on the conditions of formation and the distribution of these ion species. It is observed that the ions of clusters with an even numbered of lithium atoms are more stable than the ions of clusters with an odd numbered of lithium atoms. The clusters Li5F and Li6F were detected experimentally for the first time with their ionization energies of (4.29 +/- 0.25) eV, and (4.24 +/- 0.25) eV, respectively

Major Factors Affecting the Emission of Dilithium-Fluoride Cluster Ion in Thermal Ionization Mass Spectrometry

The process of generating dilithium fluoride ion from the samples of LiF, LiF/C-60, LIF/LiI, and LIF/LiI/C-60 using a double and a triple filament thermal ionization source for a mass spectrometer was studied. This cluster belong to the superalkali class that can form the building block for new nanoscale cluster assembled materials. The results show that in the case of the double filament thermal source when the solution of LiF/C60 was used the Li2F+ ion was detected in the longest temperature range of the evaporation filament. On the other hand, the best abundances of Li2F+ ion was obtained when the solution of LiF/C-60 were loaded on the evaporation filaments of the triple filament thermal ionization source. It has also been found that several different processes are involved in the generation of Li2F+ by the triple filament thermal source: (1) Li2F2 - GT Li2F+ + F; (2) Li+ + LiF - GT Li2F+; and (3) Li+(from LiI) + LiF - GT Li2F+. Reaction (1) is dominant at the low temperatures of evaporation filament (Te), reaction (2) it appears at Te GT 1000 degrees K, for all four above mentioned samples. Reaction (3) appears when the samples were the solution of LiF/LiI and LiF/LiI/C-60 at the high temperature of the evaporation filament

Formation and ionization energies of small chlorine-doped lithium clusters by thermal ionization mass spectrometry

RATIONALE: Theoretical calculations have shown that the first ionization energy of clusters of the type LinCl (n GT = 2), with more than eight valent electrons, is lower than that of alkali metal atoms; hence they are named superalkali. Superalkali clusters can mimic the chemical behavior of alkali metals and may be used as building blocks of new cluster-assembled materials. There is currently no reliable experimental proof of this kind of clusters and such proof is required. METHODS: The LinCl (n = 2-6) clusters were produced by a thermal ionization source of modified design, and mass selected by a magnetic-sector mass spectrometer. The modification pertains to the replacement of the side filaments by a cylinder in the triple-filament thermal ionization source. The sample, which is LiCl salt, was pressed into a ring and placed on the inner wall of the cylinder. RESULTS: It was observed that the ions of clusters with an even number of lithium atoms (Li2Cl+, Li4Cl+, Li6Cl+) are more stable than the odd-numbered ones (Li5Cl+, Li3Cl+). The ionization energies were determined to be 3.98 +/- 0.25 eV for Li2Cl, 4.10 +/- 0.25 eV for Li3Cl, 3.90 +/- 0.25 eV for Li4Cl, 4.01 +/- 0.25 eV for Li5Cl, and 4.09 +/- 0.25 eV for Li6Cl. The presence of a halogen atom reduces the ionization energy of the metal clusters. CONCLUSIONS: The thermal ionization source of modified design presents a suitable simple way to obtaining and measuring the ionization energies of very small lithium monochloride clusters. Clusters LinCl, n = 4 to 6, were detected for the first time. Copyright (C) 2012 John Wiley and Sons, Ltd

Major Factors Affecting the Emission of Dilithium-Fluoride Cluster Ion in Thermal Ionization Mass Spectrometry

The process of generating dilithium fluoride ion from the samples of LiF, LiF/C-60, LIF/LiI, and LIF/LiI/C-60 using a double and a triple filament thermal ionization source for a mass spectrometer was studied. This cluster belong to the superalkali class that can form the building block for new nanoscale cluster assembled materials. The results show that in the case of the double filament thermal source when the solution of LiF/C60 was used the Li2F+ ion was detected in the longest temperature range of the evaporation filament. On the other hand, the best abundances of Li2F+ ion was obtained when the solution of LiF/C-60 were loaded on the evaporation filaments of the triple filament thermal ionization source. It has also been found that several different processes are involved in the generation of Li2F+ by the triple filament thermal source: (1) Li2F2 - GT Li2F+ + F; (2) Li+ + LiF - GT Li2F+; and (3) Li+(from LiI) + LiF - GT Li2F+. Reaction (1) is dominant at the low temperatures of evaporation filament (Te), reaction (2) it appears at Te GT 1000 degrees K, for all four above mentioned samples. Reaction (3) appears when the samples were the solution of LiF/LiI and LiF/LiI/C-60 at the high temperature of the evaporation filament