Gerald D. Flesch

A secondary isotopic standard for 6Li/7Li determinations

A thirteen kilogram sample of highly purified Li2CO3 prepared from virgin ores has been assayed to have an absolute 6Li/7Li abundance ratio of 0.0832±0.0002. This value was determined by a mass spectrometric comparison with a primary standard blended from specially prepared, highly enriched, well-characterized isotopic materials. The abundance ratio of the primary standard was 0.083656±0.000003. The instrumental bias of the mass spectrometer was determined from isotopic ratio measurements of four primary standards having 6Li abundances in the 7–8% range.

The positive and negative ion mass spectra of chromyl chloride and chromyl fluoride

Abstract A mass spectral study of CrO 2 Cl 2 and CrO 2 F 2 has been made to illustrate the use of a positive—negative ion mass spectrometer as a convenient tool for obtaining positive and negative ion mass spectral and ionization efficiency data. Charge and atom exchange reactions have been observed and explained on the basis of ionization efficiency data. The spectrum of negative ions observed for 70 V electrons is shown to result from secondary electrons ejected from metallic surfaces. After correction of AP(Cr + ) by 2.76 eV for probable excitation, bond dissociation energies, ionization potentials and electron affinities were calculated for all the neutral fragments of CrO 2 X 2 produced in the mass spectrometer. The value of Δ H o f (CrO 2 F 2 ) was found to be −9.1 eV (−210 kcal/mole). The uncertainty of this and the other calculated thermochemical values is estimated conservatively to be 0.5 eV (±11 kcal) or less.

A mass spectrometer for the characterization of neutral species produced in the electron bombardment of gases

Abstract A mass spectrometer which permits the direct study of neutral species produced by the electron bombardment of gases is described. Functionally, it consists of an ion source with two independent electron beams, a quadrupole mass filter, and a phase-sensitive ion detector. The instrument provides for automatic scanning and recording of mass spectra and ionization efficiency data for the neutral species produced in one electron beam (pulsed at 260 Hz) and subsequently ionized in the other electron beam. The mass spectrum of the neutral species obtained from the electron bombardment of benzene, along with the ionization efficiency data for the neutral species, are presented to demonstrate the quality of the data obtained.

A 15-cm radius mass spectrometer which simultaneously collects positive and negative ions

Abstract A mass spectrometer which simultaneously extracts positive and negative ions from a single electron beam is described. Its features include: ready accessibility to the ion source and collectors, convenient attainment of alignment, simultaneous display of positive and negative ion spectra, and direct plotting of ionization efficiency data.

Neutral-fragment mass spectra of the tetramethyl compounds of the group IV a elements

Abstract A neutral-fragment mass spectrometer capable of simultaneous mass analysis of positive ions and neutral fragments resulting from interactions of electrons and molecules has been used to characterize the unimolecular decompositions of the tetramethyl derivatives of C, Si, Ge, Sn, and Pb. Four different kinds of neutral species have been observed, the most abundant being excited M(CH3)4*. Methyl radicals produced from these compounds by dissociative ionization are vibrationally excited in a state corresponding to the first symmetrical stretch. Atomic ions, Ge+, Sn+, and Pb+, are formed by dissociative ionization and from an autoionizing state.

The characterization of neutral species formed by electron impact on methane, ethane, propane, isobutane, and neopentane

Abstract The abundances of neutral species generated by electron impact on the title gases increase as each of the hydrogens of methane is systematically replaced by methyl. The most abundant species are P, (P-H), (P-H 2 ), (P-CH 3 ), and (P-CH 4 ). The observed ionization energies for H 2 and ·CH 3 indicate that each is formed in a vibrationally excited state. All other fragments are formed in the ground state of the isomeric form of lowest energy. The observed appearance energies for the neutral fragments show that the fragments are formed as products of dissociative ionization reactions.

Fragmentation reactions in the mass spectrometer for C2-C5 alkanes

Deconvolution–convolution techniques have been used to extract information from ionization efficiency data concerning the chemical decomposition of the molecular and fragment ions of the C2-C5 alkanes which occurs in the electron impact ion source of a mass spectrometer. The extracted data indicate that many of the observed ions are produced by two or more chemically different decompositions, and evidence for isomeric structures of some ions is presented. Ionization efficiency data calculated from the fragmentation schemes presented are in excellent agreement with the observed data over the 18 eV range of electron energies immediately above the ionization potential of the molecule.

Characterization of neutral species observed in the electron bombardment of methane, silane and germane

Abstract A neutral fragment mass spectrometer has been used to investigate long-lived, excited state, neutral products of the electron impact ionization of methane, silane and germane. Rydberg states of H** are observed for all three gases, while Rydberg states of Si** and Ge** are observed for silane and germane. Evidence for Rydberg states of polyatomic species is presented for silane and germane.

Model of a Mass Spectrometer which Simultaneously Collects Positive and Negative Ions

A model of a mass spectrometer which detects positive and negative ions simultaneously has been built and tested. The ion source consists of two conventional Nier‐type sources arranged back to back in which the electron gun is maintained at ground potential and the ion accelerating electrodes either positive or negative with respect to ground. Positive ions are extracted in one direction and negative ions in the diametrically opposite direction. Mass separation is achieved by means of two 180° magnetic sectors with an ion trajectory radius of 1½ in. Mass resolution of approximately 1/60 has been obtained. Mass spectra are scanned magnetically. The model has served well to aid in the solution of circuit problems which will be encountered in a large model of the instrument. Results have been obtained on the mass spectra of chromyl fluoride, CrO2F2, and Freon 12, CCl2F2, which satisfy the original design objectives for the model. Some crude appearance potentials have been attempted for the observed positive ...

The characterization of neutral species formed by electron impact on ethene, propene, isobutene, cis-2-butene and trans-2-butene

Abstract The principal neutral fragments observed during the bombardment of ethene, propene, isobutene, cis-2-butene and trans-2-butene with 20 eV electrons are (M-H)., (M-H2), (M-CH3)., (M-CH4), CH3. and (C3H3).. The abundance of neutral fragments generated increases with molecular weight. The neutral fragments are isomers of lowest ionization energy and most are formed in vibrationally excited states. The average appearance energy of the various neutral fragments observed is 9.2±1.4 eV which is evidence that the observed fragments are formed by dissociative excitation rather than dissociative ionization.