Robert W. Kiser

Ions produced in the mass spectrometer from cyclopentadienylmetal carbonyl compounds of cobalt, manganese and vanadium

Abstract The positive and negative ions formed from (C 3 H 3 )Co(CO) 2 , (C 3 H 3 Mn(CO) 3 and (C 3 H 3 )V(CO) 4 upon electron impact in the mass spectrometer have been investigated. Separation of the carbonyl groups in preference to the cyclopentadienyl ring system from the remainder of the molecular ion was found to occur. Ionization potentials of 8.3 ≠ 0.2, 8.3 ≠ 0.4 and 8.2 ≠ 0.3 eV were determined for cyclopentadienylcobalt dicarbonyl, cyclopentadienylmanganese tricarbonyl and cyclopentadienylvanadium tetracarbonyl, respectively. A discussion of the probable processes of ionization and dissociation, consistent with the observed energetics, is presented and the thermochemical data for D [(C 3 H 3 )-M + ] and D [(C 3 H 3 )-M + ] are considered.

Unimolecular Decomposition of Negative Ions Formed from the Transition‐Metal Carbonyls of Ni, Fe, Cr, Mo, and W

Negative‐ion mass spectra and dissociative electron‐capture energetics for the principal metal‐containing ions have been determined for nickel tetracarbonyl, iron pentacarbonyl, chromium hexacarbonyl, molybdenum hexacarbonyl, and tungsten hexacarbonyl. These data are utilized in the first application of the statistical theory of mass spectra to describe the unimolecular decompositions of negative ions. The mechanism proposed for the formation of the various M(CO)x− ions is an ion‐pair production process followed by a series of consecutive ionic‐unimolecular decomposition reactions involving the elimination of CO groups.

The formation of gaseous ions from dicyclopentadienyltitanium dichloride and dicyclopentadienylzirconium dichloride upon electron impact

Abstract The mass spectra of dicyclopentadienyltitanium dichloride and dicyclopentadienylzirconium dichloride are characterized by a unique fragmentation scheme involving the removal and fragmentation of the cyclopentadienyl groups in the molecular ions. From heats of combustion the heat of formation of Ti(C 5 H 5 ) 2 Cl 2 (s) and Zr(C 5 H 5 ) 2 Cl 2 (s) were determined to be -145 and -153 kcal/mole, respectively. The measured ionization potentials are I [Ti(C 5 H 5 ) 2 Cl 2 ] = 8.9 8 ±0.1 6 and I [Zr(C 5 H 5 ) 2 Cl 2 ] = 9.3 7 ±0.2 5 eV, respectively. Metastable transitions observed were used together with clastogram data to identify the fragmentation routes of the principal ionic species.

Ionization and fragmentation of dimethylzinc, trimethylaluminum, and trimethylantimony☆

Ionization and appearance potentials determined with a time-of-flight mass spectrometer are reported for the principal positive ions in the mass spectra of dimethylzinc, trimethylaluminum, and trimethylantimony. The heats of formation, deduced by the application of the experimentally determined energetics and additional thermochemical data, have been listed for the principal positive ions of the three metal alkyls. The observed ionization potentials for Zn(CH3)2 (8.86±0.15 eV), Al(CH3)3 (9.09±0.26 eV), and Sb(CH3)3 (8.04±0.16 eV) are compared to the ionization potentials reported previously for methyl-substituted metal compounds. Additionally, the ionization potentials of the following radicals have been estimated: Zn(CH3) ⋍ 9.2 eV; Al(CH3)2 ⋍ 6.6 eV; AlCH3 ⋍ 7.8 eV; Sb(CH3)2 ⋍ 7.7 eV; and SbCH3 ⋍ 9.4 eV.

Studies of the Shapes of Ionization-Efficiency Curves of Multiply Charged Monatomic Ions. I. Instrumentation and Relative Electronic-Transition Probabilities for Krypton and Xenon Ions

The determination of threshold ionization potentials for multiple ionization processes in krypton and xenon is shown to depend upon the threshold law assumed for these processes. Support has been obtained for the kth power rule for k‐fold ionization by electron impact. Ionization potentials have been obtained for multiple ionization in these gases. It was found that the output electron current of the magnetic electron multiplier, obtained for the multiply charged positive ions, depends strongly upon the charge of the ion impinging upon the ion cathode of the multiplier.

Metastable Transitions Observed in a Time‐of‐Flight Mass Spectrometer

A time‐of‐flight mass spectrometer has been employed in the investigation of metastable transitions by using a retarding potential technique. Expressions have been developed which permit a simple, nearly quantitative determination of the masses of the daughter ions arising from these transitions. In addition equations are derived which permit the identification of charge exchange reactions, An++B→Ap++B(n—p)+. Most of the metastable transitions observed using magnetic instruments have either been determined or accounted for by this method in n‐butane, ethyl acetate, trimethyl phosphate, and dimethylmethylphosphonate. In addition, this approach has the unique feature of permitting the observation of new metastable transitions not observed in magnetic instruments. The limitations of the method are recognized and discussed.

ESTIMATION OF THE IONIZATION POTENTIAL AND DISSOCIATION ENERGY OF MOLECULAR ASTATINE

The ionization potential and dissociation energy are estimated for astatine from empirical correlations. From the /sub e values for the lighter halogens, the e/ for At/sub 2/ is estimated to be 160 cm/sup -1/, and a plot of these /sub e/ values on a log /sub e/ vs. log n/sup 2/I graph (n = principal quantum number)

Characteristic parameters of geigermüller counter gases. Propane-argon and propane-helium mixtures

SummaryThe combination of the Wilkinson and the Diethorn-Kohman expressions of counter operation was tested under conditions in which different rare gases were used with the same quench gas as Geiger-Müller counter fillings. The gas multiplication factor was assumed to be a constant equal to 107 and the results obtained again appear to substantiate this choice. The physical significance of the parameters involved in the theoretical expression are related to the ionization cross sections and the energy necessary to produce an ion pair in the gases used. The results of the present study appear to substantiate the approach taken in the earlier work.