Molecular Structure Effects on the Free‐Ion Yields and Reaction Kinetics in the Radiolysis of the Methyl‐Substituted Propanes and Liquid Argon: Electron and Ion Mobilities

1972 ◽  
Vol 56 (5) ◽  
pp. 2333-2341 ◽  
Author(s):  
P. G. Fuochi ◽  
G. R. Freeman
Keyword(s):  
Molecular Structure ◽  
Reaction Kinetics ◽  
Liquid Argon ◽  
Free Ion ◽  
Ion Yields

Comparison between Molecular Structure Effects in Triplet Positronium Annihilation Rates and Radiolysis Free Ion Yields in Liquid Hydrocarbons

1972 ◽  
Vol 50 (16) ◽  
pp. 2697-2698 ◽  
Author(s):  
G. R. Freeman ◽  
J.-P. Dodelet
Keyword(s):  
Molecular Structure ◽  
Chain Length ◽  
Molecular Interaction ◽  
Half Life ◽  
Density Effect ◽  
Liquid Hydrocarbons ◽  
Positronium Annihilation ◽  
Free Ion ◽  
Alkane Chain ◽  
Ion Yields

Two seemingly unrelated phenomena in liquid hydrocarbons have similar trends in their dependences upon the molecular structure of the hydrocarbon. The phenomena are the annihilation half-life of triplet positronium and the radiolysis free ion yield. In n-alkanes the effect of increasing the molecular chain length, upon both phenomena, appears to be simply to increase the density of interacting sites. Branching the alkane chain decreases the strength of molecular interaction with both electrons and positronium, although the relative decrease is much greater for the former than for the latter. The effects of double bonds on the phenomena, after separating out the density effect, are different from each other.

Effect of Electric Field Strength on the Free Ion Yields in the X-Radiolysis of Liquids: Influence of Molecular Structure and Temperature

1972 ◽  
Vol 50 (11) ◽  
pp. 1617-1626 ◽  
Author(s):  
J.-P. Dodelet ◽  
P. G. Fuochi ◽  
G. R. Freeman
Keyword(s):  
Field Strength ◽  
Liquid Argon ◽  
Separation Distance ◽  
Relative Increase ◽  
Distribution Functions ◽  
Electron Pairs ◽  
Gaussian Distribution Function ◽  
Free Ion ◽  
Liquid Methane ◽  
Ion Yields

The relative increase in the free ion yield with increasing field strength E, expressed as [Formula: see text] is smaller when the following quantities are larger: (1) dielectric constant, (2) temperature, and (3) separation distance between the geminate ion–electron pairs. The field dependence [Formula: see text] equals 9.7/εT2 cm/V at low E, but at higher fields it is affected by the above three factors and by E itself. Results obtained from the liquids propane (123–233 °K), 2-methylpropane (isobutane, 148–294 °K), 2,2-dimethylpropane (neopentane, 295 °K), argon (87 °K), oxygen (87 °K) and argon–oxygen solutions (87 °K) are presented and analyzed according to a theoretical model. Several types of ion–electron separation (y) distribution functions are tested. Within the framework of the model a power function F(> y) = yminy−x with x < 4 provides a good interpretation of the results when [Formula: see text] a Gaussian distribution function provides the best interpretation of the field effects when [Formula: see text] Either the y distribution has a Gaussian core with a more gently sloping tail, or distributions are more Gaussian-like in liquids in which the electron ranges are greater. The electron range in pure argon (b = 1300 Å) is much smaller than had been expected and is only 2.6 times greater than that in liquid methane (b = 500 Å at 120 °K). Phonon emission by 10–0.01 eV electrons in liquid argon may be relatively efficient and might involve transient states of the type [Formula: see text]

Low energy electron ranges in liquids: determination by nonhomogeneous kinetics

1977 ◽  
Vol 55 (11) ◽  
pp. 2050-2062 ◽  
Author(s):  
J.-P. Dodelet
Keyword(s):  
Critical Temperature ◽  
Melting Point ◽  
Distribution Functions ◽  
Liquid Density ◽  
Range Distribution ◽  
Total Ionization ◽  
Free Ion ◽  
Drastic Increase ◽  
Pass Through ◽  
Ion Yields

Free ion yields have been measured in four hydrocarbon liquids: n-pentane, cyclopentane, neopentane, and neohexane. Each liquid has been studied from room temperature or below up to the critical temperature. Theoretical curves have been calculated using the relation between the free ion yields and the external field strength derived by Terlecki and Fiutak on the basis of an equation by Onsager. Two popular electron range distribution functions, Gaussian and exponential, have been shown not to be an adequate representation of the reality as far as the model used for the calculations is concerned. In order to fit experimental points, both range distribution functions would require a drastic increase in the total ionization yield, Gtot, with temperature increase. This would mean an unrealistic decrease of the ionization potential of the molecule from the melting point up to the critical temperature.It is possible to keep Gtot quite constant and within the range of values obtained by other techniques by extending the Gaussian range distribution function with a (range)−3 probability tail. The most probable range can be normalized for the liquid density. This parameter has been used to obtain information about the behaviour of epithermal electrons in the four alkane liquids from the melting point up to the critical temperature.(1) Normalized penetration ranges of epithermal electrons are dependent on the structure of the molecule in the entire liquid range but differences are smaller at critical than at low temperatures.(2) Normalized penetration ranges of epithermal electrons pass through a maximum in the liquid phase for neopentane, neohexane, and cyclopentane. No maximum is observed for n-pentane.(3) There is no drastic change in the behaviour of epithermal electrons in these alkanes at the critical temperature.

scholarly journals The Ion Pair Thermal Model of MALDI MS

2021 ◽  
Author(s):  
Shiyue Fang
Keyword(s):  
Gas Phase ◽  
Thermal Model ◽  
Ion Pair ◽  
Pair Formation ◽  
Maldi Ms ◽  
Ion Extraction ◽  
Free Ion ◽  
Pair Separation ◽  
Ion Yields ◽  
Ion Pair Separation

The ion pair thermal model for MALDI MS is described. Key elements of the model include thermal desorption and ionization, strong tendency to neutralization via ion pair formation and proton transfer in the gas phase, thermal equilibrium, overall charge neutral plume, and thermal energy assisted free ion generation via ion pair separation by ion extraction potential. The quantities of ions in the solid sample and in the gaseous plume are estimated. Ion yields of different classes of molecules including peptides, nucleic acids, permanent salts and neutral molecules are estimated at the macroscale and single ion pair levels. The estimated ion yields are close to experimentally observed values under certain assumptions. Explanations of several observations in MALDI MS such as mostly single-charged peaks, improvement of spectra by ammonium cation, and ion suppression are provided. We expect that the model can give insights for the design of new conditions and systems for improving the sensitivity and resolution of MALDI MS and improving its capability and reliability to analyze large biomolecules.

X-Radiolysis Ion Yields and Electron Ranges in Liquid Xenon, Krypton, and Argon: Effect of Electric Field Strength

1973 ◽  
Vol 51 (5) ◽  
pp. 641-649 ◽  
Author(s):  
Maurice G. Robinson ◽  
Gordon R. Freeman
Keyword(s):  
Field Strength ◽  
Gas Phase ◽  
Electric Fields ◽  
Zero Field ◽  
Energy Effect ◽  
Secondary Electrons ◽  
Total Ionization ◽  
Field Dependent ◽  
Free Ion ◽  
Ion Yields

X-Radiolysis ion yields were measured at electric fields between 1 and 60 kV/cm in argon at 87 °K, krypton at 148 °K, and xenon at 183 °K. The results were analyzed according to a theoretical model to obtain the total ion yields Gtot,the free ion yields at zero field strength Gfi0 and the most probable penetration ranges b of the secondary electrons in the liquids. The respective values were: Ar, 7.3, 2.9, 1330 Å; Kr, 13.0, 5.8, 880 Å; Xe, 13.7, 7.0, 720 Å. The total ionization yields in these substances are greater in the liquid than in the gas phase, probably due to smaller ionization potentials in the condensed phase (polarization energy effect). Field dependent electron mobilities are also reported.

Yields of Free Ions in the X Radiolysis of Some Simple Saturated and Unsaturated Hydrocarbon Liquids: Effects of Molecular Structure and Temperature

1971 ◽  
Vol 49 (22) ◽  
pp. 3657-3664 ◽  
Author(s):  
M. G. Robinson ◽  
P. G. Fuochi ◽  
G. R. Freeman
Keyword(s):  
Molecular Structure ◽  
Interaction Model ◽  
Unsaturated Hydrocarbon ◽  
The Other ◽  
Coulombic Interaction ◽  
Secondary Electrons ◽  
Free Ions ◽  
Free Ion ◽  
Liquid Methane ◽  
Hydrocarbon Molecules

Pulse techniques were used at temperatures ranging from 120 to 293 °K. A quasifree electron conductance transient (k/u overshoot) was observed in liquid methane, but not in ethane, propane, cyclopropane, ethylene, propylene or butene-1. The free ion yield in methane, Gfi = 0.8 at 120 °K, is much larger than those in the other liquids, which at 183°K are: ethane, 0.13; propane, 0.076; cyclopropane, 0.04; ethylene, 0.017; propylene, 0.04; butene-1, 0.027. The activation energies of free ion formation are, in kcal/mol: ethane, 0.6; propane, 0.8; ethylene, 0.5; propylene, 1.0; butene-1, 1.0. The results are interpreted in terms of the coulombic interaction model. The distances that the secondary electrons penetrate the liquid away from their parent ions are greater when the hydrocarbon molecules are more sphere-like, and are reduced by the presence of a π bond in the molecule. Cyclopropane behaves somewhat like an olefin in this regard, a fact that is explained by the unusual bonding in the C3 ring. In the present liquids the only ionization events that contribute appreciably to the free ion yield are those in which the electron penetrates [Formula: see text] from the parent ion.

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