Search results for " ionization"
showing 10 items of 621 documents
Liquid chromatographic–mass spectrometric determination of post-harvest fungicides in citrus fruits
2001
Liquid chromatography (LC)-atmospheric pressure ionisation (API)-mass spectrometry (MS) has been used to determine residues of five fungicides in oranges with a minimum sample cleanup. Atmospheric pressure chemical ionisation (APCI) and electrospray (ES) were compared and both gave similar results in terms of sensitivity and structural information. The main ions were [M+H]+ for carbendazim, imazalil, thiophanate methyl and thiabendazole, and [M+H-C4H9NHCO]+ for benomyl. Samples were extracted with sodium sulphate and ethyl acetate. Although benomyl and thiophanate methyl were transformed through the extraction procedure to carbendazim, the method showed good precision (13%) and recovery (70…
The fragmentation of 5- and 3-substituted thiophene-2-carboxamides under electron impact
1980
The 70 eV electron impact mass spectra of twelve 5- and 3-substituted thiophene-2-carboxamides are discussed with the aid of exact mass measurements and labelling experiments. All mass spectra exhibit pronounced molecular ions. Some isomeric 5- and 3-substituted title compounds can be differentiated by mass spectrometry. The fragmentation is influenced by a strong ‘ortho-effect’ which activates the NH3 elimination. In the other cases the most important fragmentation is NH2˙ loss, followed by CO elimination.
Multicollision-induced dissociation of multiply charged gold clusters, Aun2+, n = 7–35, and Aun3+, n = 19–35
2000
Abstract Multicollision-induced dissociation (MCID) has been applied to gold clusters, Au n 2+ (n = 7–35) and Au n 3+ (n = 19–35) stored in a Penning trap. By application of ion cyclotron resonance excitation and pulses of argon collision gas, fragmentation yields have been measured as a function of the clusters’ kinetic energy. The corresponding dissociation energies have been determined by use of the impulsive collision theory and the quantum Rice–Ramsperger–Kassel (RRK) model for the energy transfer to internal cluster modes and for delayed dissociation, respectively. As compared to earlier measurements of singly charged gold clusters the variation of the stability as a function of clust…
Unveiling anion-induced folding in tripodal imidazolium receptors by ion-mobility mass spectrometry.
2021
The anion-induced folding of tripodal imidazolium receptors has been investigated by NMR spectroscopy, electrospray ionization ion mobility mass spectrometry and DFT calculations. Such folding can be switched by anion release upon collision induced dissociation.
<title>Collisional and thermal ionization of sodium Rydberg atoms in single and crossed atomic beams</title>
2006
The results of the experimental and theoretical study on associative ionization of laser excited Na Rydberg atoms in collisions with ground-state atoms and on thermal ionization by blackbody radiation in single and crossed effusive atomic beams are reported and discussed.
Direct observation of second-order atom tunnelling
2007
Tunnelling of material particles through a classically impenetrable barrier constitutes one of the hallmark effects of quantum physics. When interactions between the particles compete with their mobility through a tunnel junction, intriguing novel dynamical behaviour can arise where particles do not tunnel independently. In single-electron or Bloch transistors, for example, the tunnelling of an electron or Cooper pair can be enabled or suppressed by the presence of a second charge carrier due to Coulomb blockade. Here we report on the first direct and time-resolved observation of correlated tunnelling of two interacting atoms through a barrier in a double well potential. We show that for we…
EBIT trapping program
1993
The LLNL electron beam ion trap provides the world's only source of stationary highly charged ions up to bare U. This unique capability makes many new atomic and nuclear physics experiments possible.
Strong enhancement of Penning ionization for asymmetric atom pairs in cold Rydberg gases: the Tom and Jerry effect
2016
We consider Penning ionization of Rydberg atom pairs as an Auger-type process induced by the dipole–dipole interaction and employ semiclassical formulae for dipole transitions to calculate the autoionization width as a function of the principal quantum numbers, n d , n i , of both atoms. While for symmetric atom pairs with the well-known increase of the autoionization width with increasing n 0 is obtained, the result for asymmetric pairs is counterintuitive—for a fixed n i of the ionizing atom of the pair, the autoionization width strongly increases with decreasing n d of the de-excited atom. For H Rydberg atoms this increase reaches two orders of magnitude at the maximum of the n d depende…
Tetranitroresorcin[4]arene: synthesis and structure of a new stereoisomer
2009
The direct reaction between 2-nitroresorcinol and acetaldehyde in alkaline medium yields tetranitro-C1-resorcin[4]arene in a moderate 8.2% overall yield which was characterized by single crystal X-ray crystallography, 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS). In solution and in the solid state, the product adopts a unique, thermally stable and unprecedented rcct-boat conformation.
[Ag67(SPhMe2)32(PPh3)8]3+: Synthesis, Total Structure, and Optical Properties of a Large Box-Shaped Silver Nanocluster
2016
Engineering the surface ligands of metal nanoparticles is critical in designing unique arrangements of metal atoms. Here, we report the synthesis and total structure determination of a large box-shaped Ag67 nanocluster (NC) protected by a mixed shell of thiolate (2,4-dimethylbenzenethiolate, SPhMe2) and phosphine (triphenylphosphine, PPh3) ligands. Single crystal X-ray diffraction (SCXRD) and electrospray ionization mass spectrometry (ESI-MS) revealed the cluster formula to be [Ag67(SPhMe2)32(PPh3)8]3+. The crystal structure shows an Ag23 metal core covered by a layer of Ag44S32P8 arranged in the shape of a box. The Ag23 core was formed through an unprecedented centered cuboctahedron, i.e.,…