P. S. Rudolph

Radiolysis of Methane in a Wide‐Range Radiolysis Source of a Mass Spectrometer. I. Individual and Total Cross Sections for the Production of Positive Ions, Negative Ions, and Free Radicals by Electrons

The abundances of, and the total and individual cross sections for, primary products (positive ions, neutral species, and negative ions) resulting from elementary reactions induced by the absorption of energy by CH4 from ionizing radiation (100‐eV electrons) have been measured. This was accomplished with the dual electron beam section of our wide‐range radiolysis source. The results show that positive ions and free radicals are produced in nearly equal abundances, 45% and 55%, respectively. On the other hand, negative ions are less abundant by about four orders of magnitude. The total cross section for positive ionization (σI) by 100‐eV electrons is 3.8×10−16 cm2 and that for the formation of neutral species (σN) is 4.7×10−16 cm2. To independently test the reliability of the dual electron‐beam ion source, the total and individual cross sections for ionization of Ar by 100‐eV electrons were measured for comparison with published values. Our value for the total cross section (σI) of 3.24× 10−16 cm2 is in sa...

Negative Ion Mass Spectra of Hydrocarbons and Alcohols

The complete negative ion mass spectra and relative sensitivity for positive and negative ion formation in various organic compounds are herein reported for the first time. These compounds include methane, the C2— hydrocarbons, n‐butane, and all of the alkyl alcohols through the butyls. A limited comparison of the observed ionic patterns with molecular structure and chemical properties manifests a correlation. Relative sensitivities for positive and negative ion formation in these compounds show that formation of positive ions is about four orders of magnitude more probable than formation of negative ions under the conditions used in this study.

Mass Spectrometric Studies of Ionic Intermediates in the Alpha‐Particle Radiolysis of Ethylene

Two techniques were used for the elucidation of ion‐molecule reaction mechanisms in the alpha radiolysis of C2H4 in the new alpha‐particle mass spectrometer. The corresponding variations in the percent of primary, secondary, and tertiary ions over a tenfold pressure range (to 0.1 mm) were used to postulate the reaction mechanisms. Mixtures of the C2 hydrocarbons were employed to increase the relative concentrations of a specific reactant ion, thus independently confirming the postulated mechanisms. Polymeric ions as large as C5H9+ were observed. Conclusions as to reaction mechanisms drawn from this study are compared to those drawn from the appearance potential technique used in the electron impact studies. Values of the rate constants are also compared for several secondary reactions.

Mass Spectrum of Acetylene Produced by 5.1‐Mev Alpha Particles

The mass spectrum of acetylene produced by 5.1Mev alpha particles was measured and compared with that produced by 75-ev electrons. Striking differences were noted, and it is indicated that alpha-induced ionization may be useful in mass spectral analysis as well as in radiation chemistry. (T.R.H.)

Transient Species in the Radiolytic Polymerization of Cyanogen

Admixing of noble gases has caused the radiolytic polymerization rates to be increased approximately proportional to the stopping power of the gas. In the (CN)/sub 2/ + xenon system, charge transfer resulted in an increase rather than a decrease as predicted by the lower ionization potential. Because of this anomaly, the transient species produced in the (CN)/sub 2/ and (CN)/sub 2/ + xenon systems were investigated. The reactant gas was irradiated by 135-ev electrons at 1 mm pressure in the ionization chamber of a mass spectrometer. The observed transient polymer species produced in the electron-induced radiolysis of (CN)/sub 2/, as well as the absolute intensity for each species, are tabulated. When xenon was admixed with (CN)/sub 2/, the total intensity of the negative ions was markedly increased by ionization by secondary electrons from xenon and a reaction of metastable xenon* (5p/sup 5/6s) with (CN)/sub 2/ to form CN radicals, which are subsequently ionized. (B.0.G.)

Mass Spectrometric Observation of Triatomic Ions in Chlorine and Bromine Gases

A stsdy was made to determine if the triatomic ions Cl/sub 3+/ and Cl/ sub 3-/ in pure chlorine result from the ionization of neutral Cl/sub 3/, and in addition, similar observations of bromine vapor were made. The investigation failed to establish whether any of the trimeric chlorine ions were derived from neutral Cl/sub 3/. (J.R.D.)

Experimental and Theoretical Considerations for Ionization of Simple Hydrocarbons, H2, D2, O2, H2O, and the Rare Gases by 2.2‐MeV α Particles and by Electrons in a Mass Spectrometer

The measurement of ionization cross sections and mass spectra produced by 2.2‐MeV α particles is briefly discussed with emphasis on experimental details which lead to results which are more accurate than those of the previous study. Experimental techniques and apparatus have been developed and applied to these measurements for H2, D2, O2, H2O, CH4, C2H2, C2H4, C2H6, and the rare gases. The experimental results for H2 and He are compared with detailed calculations in the Born—Bethe approximation and for Ar in the classical approximation. The ionization cross sections for the removal of one electron conform rather well to the predictions although the experimental results tend to be somewhat lower, than the theoretical values. Experimental values for He, Ar, H2, and N2 are in good agreement with extrapolated data of McDaniel and co‐workers.The mass spectra produced by 2.2‐MeV α particles show the same fragments as those produced by electrons with the same velocity, but the abundance of some fragment ions dif...

Ionic Complexes of Xe and C2H2 Produced by the Radiolysis of These Gases

Binary mixtures of acetylene and the noble gases were irradiated by 90 ev electrons at pressures up to 1.3 mm in the ionization chamber of a research mass spectrometer. Various proportions of the mixtures and a range of pressures were employed in this study. Ionic complexes, [XeC2H]+ and [XeC2H2]+, were observed in the C2H2–Xe system. The intensity ratio [XeC2H2]+/[XeC2H]+ increased linearly with increasing pressure. No ionic complexes were observed in the other mixtures. A series of reactions involving Xe+ is presented.

Ion‐Molecule Charge Transfer Reactions in the Alpha Radiolysis of Various Hydrocarbons in a Mass Spectrometer

The new alpha‐particle mass spectrometer proves to be a powerful tool for the study of charge transfer between gaseous ions and molecules. Energetically possible charge‐transfer reactions have been differentiated into probable and improbable reactions by employing binary mixtures of hydrocarbon gases in this instrument.The alpha‐particle induced charge‐transfer reaction, C2H2++C6H6→C2H2+C6H6+, is shown to be very efficient. In contrast, the charge‐transfer reaction, C2H2++C2H4→C2H2+C2H4+, is shown to be inefficient. This inefficiency is discussed in terms of the competing chemical reaction, C2H2++C2H4→C3H3+ +CH3.

Kinetics of the Alpha Radiolysis of Carbon Monoxide

The radiolytic decomposition of CO induced by alpha particles appears to be initiated by two reactive species, CO+ and CO*. The products of the reaction are CO2 and the solids (C3O2)x and graphite. Carbon dioxide formed during the reaction depletes the CO+ by charge transfer. Thus, when CO2 pressure becomes sufficiently high, CO* only initiates reaction. The reaction mechanism suggested is consistent with previous ionization and photochemical studies in the CO system.