C. E. Melton

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...

STUDY BY MASS SPECTROMETRY OF THE DECOMPOSITION OF AMMONIA BY IONIZING RADIATION IN A WIDE-RANGE RADIOLYSIS SOURCE.

A wide‐range radiolysis source which can be used to approximate an ideal experimental study of a chemical reaction induced by ionization has been designed and constructed for a study of the decomposition of ammonia. The source consists of three separate compartments in series, each with a separate electron beam which can be independently controlled over a wide range of intensity and energy. The pressure in the source can be varied over a range of 10−9 to 10 torr and decreases progressively from compartment to compartment. Reactions can be followed in time starting from about 10−14 sec after irradiation up to the time for the formation of final stable products. Each compartment has a distinct function and is used to observe reactions which occur at different times after irradiation. Compartment 3 is a high‐sensitivity ion source which ionizes reaction products produced in a preceding compartment for mass identification by a sensitive mass spectrometer to which the apparatus is attached. Also, cross section...

Mass‐Spectrometric and Theoretical Evidence for NH4 and H3O

The unusual chemical species H3O and NH4 have been studied using both experimental and theoretical methods. Experimentally the species were investigated by means of a mass spectrometer equipped with two different reactors designed to produce reactive species. The NH4 was produced by surface chemistry techniques, whereas H3O was produced by irradiating water vapor with ionizing electrons. A study of the ionization potential of NH4 by surface ionization techniques gave a value of 5.9 eV. The ionization potential of H3O was measured by conventional techniques and a value of 10.9 eV was obtained. In the theoretical investigation, the physical parameters are given including s‐, p‐, and d‐type orbitals for H3O and s‐, p‐, and f‐type orbitals for NH4. The calculations for NH4 predict a tetrahedral structure with internuclear distances of about 1.06 A and they predict a planar H3O molecule with bond distances about 1.03 A. The ionization potentials of H3O and NH4 were estimated to 3.9 and 3.0 eV.

Charge Transfer Reactions Producing Intrinsic Chemical Change: Methyl, Methylene, and Hydrogen Radicals Produced from Argon and Methane Reactions

Charge transfer reactions producing intrinsic chemical changes in the neutral molecule have been proven by mass spectrometric techniques. The charge transfer reaction Ar++CH4→Ar+CH3++H producing an intrinsic chemical change in CH4 was found to be more probable by a factor of five than the simple charge transfer reaction Ar++CH4→Ar+CH4+. Charge transfer reactions in mixtures of Ar and CH4 and Kr+CH4 were studied over the pressure range of 0.1–0.5 mm of Hg in the ionization chamber. Reactions were elucidated by catalytic and negative ion studies as well as by the usual pressure and appearance potential techniques. In the Kr+CH4 mixture, the reaction Kr++CH4→Kr+CH3++H producing the charged radical CH3+ was found to have a high probability. Absolute values for rate constants and cross sections are given for all of the charge transfer reactions observed in the Ar+CH4 mixture. Products from these elementary charge transfer reactions are correlated to previously reported radiolytic, α ionization (W value), and h...

Metastable Transitions and Collision‐Induced Dissociations in Mass Spectra

A number of new metastable transitions have been identified in the mass spectra of n‐butane and i‐butane. The appearance of various metastable transitions was discussed in terms of the quasi‐equilibrium theory of mass spectra and the energetics of ionic decomposition processes. A study of the pressure independence of metastable transitions revealed the existence of several collision‐induced dissociations. Some similarities of these processes to electron impact‐induced dissociations were pointed out. Approximate relative cross sections were determined for the various collision processes.

Dissociation of CO+ and CO++ Ions by Collision with Neutral Molecules

The dissociations of CO+ and CO++ ions by ion‐molecule collision have been investigated with a mass spectrometer. CO+ dissociates into C+ and O, or C and O+, depending upon the energy of the parent ion. The predominant ion resulting from dissociation of CO++ is C+ suggesting a charge‐exchange dissociation reaction. This is supported by the observation that neutral molecules having high ionization potentials such as He and Ne do not produce dissociation in CO++. Energy for the dissociation of CO++ is derived from the electronic energy of the molecular ion rather than from kinetic energy.

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.

Collision‐Induced Dissociations in the Mass Spectrum of Acetylene

The mass spectrum of methane has been investigated in the pressure range 1×10—7 to 5×10—5 mm of Hg. A number of diffuse peaks were observed at nonintegral masses. These arise from dissociation of various ionized methane fragments on collision with residaul methane gas in the field‐free region of the mass spectrometer. The linear pressure dependence of their relative abundance points to single‐collision processes. No multiple‐collision processes or truly unimolecular metastable transitions were observed. A parallel between electron impact and collision‐induced dissociation is pointed out.

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.)