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.

Effect of density on the total ionization yields in X-irradiated argon, krypton, and xenon

1977 ◽  
Vol 55 (11) ◽  
pp. 1838-1846 ◽  
Author(s):  
Sam S.-S. Huang ◽  
Gordon R. Freeman
Keyword(s):  
Field Strength ◽  
Gas Phase ◽  
Excited States ◽  
Electric Fields ◽  
Energy Gap ◽  
Low Density ◽  
Infinite Field ◽  
Free Ions ◽  
Total Ionization ◽  
Higher Excited States

The amounts of ionization produced by absorption of X radiation in the liquids xenon, krypton, and argon are respectively 1.5, 1.4, and 1.2 times greater than those produced by the absorption of the same energy in the corresponding low density gases. The yields of free ions in the irradiated liquids were measured at applied electric fields 1–40 kV/cm and extrapolated to infinite field strength. The total number of ionizations per 100 eV absorbed was Gtot = 6.6 in xenon, 6.0 in krypton, and 4.5 in argon. The reason that the ionization yield is larger in the liquid than in the corresponding low density gas is partly that the energy gap Eg between the top of the valence band and the bottom of the conduction band in the liquid is smaller than the gas phase ionization potential IP. The ratio IP/Eg = 1.36 for xenon (Roberts and Wilson), 1.27 for krypton, and 1.17 for argon (from data of Jortner et al.). An extra source of ionization in the liquid might be reaction of the higher excited states, M* + M → [M2+ + e−].

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.

scholarly journals Zur Kinetik des monomolekularen Zerfalls organischer Ionen in hohen elektrischen Feldern

1966 ◽  
Vol 21 (11) ◽  
pp. 1920-1930
Author(s):  
H. D. Beckey ◽  
H. Knöppel
Keyword(s):  
Field Strength ◽  
Electric Fields ◽  
Mass Spectra ◽  
Resolving Power ◽  
Field Ionization ◽  
Time Interval ◽  
Dissociation Limit ◽  
Zero Field ◽  
Minute Amount ◽  
Molecular Ion

The kinetics of unimolecular decomposition of organic ions in the presence of electric fields up to 108 V/cm is discussed. The results are deduced from the mass spectra obtained by field ionization of organic molecules. The time interval between formation and decomposition of the ions can be derived from the shape of the mass lines. It is shown that field induced decomposition can occur at a minimum time of about 3 · 10–14 sec after field ionization. The optimum time resolution with these experiments, 10–12 sec, is given by the resolving power of the mass spectrometer.The results can be interpreted in terms of five different mechanisms :1. Field induced dissociation. Excitation of the molecular ion to a state above the dissociation limit is possible at high enough fields. Spontaneous dissociation within one vibrational period will then be possible because the excitation energy is contained in the reaction coordinate.2. Field induced dissociation by tunneling of radicals through the potential barrier. This may occur after excitation of the molecular ion to a state lying in an interval between the dissociation limit and about half a vibrational energy quantum below this, provided the field strength is high enough. The maximum observable life time of ions resulting from this process is about 6·10–12 sec.3. Field induced dissociation, delayed by re-orientation of the molecular ion. Certain orientations of the molecular ion are favoured with respect to field dissociation. The maximum re-orientation time for a favourable position is of the order 3·10–12 sec.4. Field induced statistical dissociation. This is due to fluctuation of energy within the ion, as in the case of common reaction kinetics, but with lowering of the dissociation limit by the field. The time intervall for these processes lies between about 10–13 and 10–11 sec.5. Statistical decomposition in the space of low or zero field strength. This process is due to energy fluctuation within the molecular ion excited to a state above the dissociation limit, lowered only by a minute amount by the weak field. The range of life times is about 10–11 to 10–8 sec. Processes of the same type, occurring at zero field strength within about 10–8 and 10–6 sec, are called — as usually — “metastable” processes.The processes described here are derived mainly from the FI mass spectra of paraffins, alcohols, ethers and ketones. Dissociation is hindered, in some cases, by high electric fields.

Electron thermalization distances and free-ion yields in dense gaseous and liquid benzene

1992 ◽  
Vol 70 (6) ◽  
pp. 1618-1622 ◽  
Author(s):  
Norman Gee ◽  
Gordon R. Freeman
Keyword(s):  
Three Dimensional ◽  
Dielectric Constants ◽  
Zero Field ◽  
Fluid Density ◽  
Model Assumption ◽  
Liquid Benzene ◽  
Free Ion ◽  
Ion Yields ◽  
Yield Formula ◽  
Reduced Density

Electron thermalization has been studied in gaseous and liquid benzene at 4.1 ≤ d/kg m−3 ≤ 878 (temperatures 295–560 K) using measurements of the free-ion yield [Formula: see text] as a function of electric field strength E and temperature T. The measured [Formula: see text] values at each T were compared to those calculated using an extended Onsager model. Assumption of a three-dimensional Gaussian distribution of secondary electron thermalization distances YG resulted in too large a field dependence. The Gaussian with the small added tail, YGP, gave the correct dependence. Values of the yield extrapolated to zero field, [Formula: see text] and of the most probable thermalization distance bGP were obtained. Variation of the density-normalized distance bGPd with reduced density d/dc (dc = critical fluid density) was expected to be similar to that in ethene, due to the π-electrons in the two compounds. Instead, it was similar to that in ethane. Throughout the liquid range, epithermal electrons were de-energized less efficiently than in the gas at d < 0.5 dc where the benzene molecules are further apart. As the density increases above 2 dc the values of bGPd decreased as in other hydrocarbons, rather than like those in hexafluorobenzene, which increased sharply. Dielectric constants were also measured up to 560 K.

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]

Electron thermalization-distance distributions in electron-attaching fluids

1990 ◽  
Vol 68 (9) ◽  
pp. 930-934 ◽  
Author(s):  
Norman Gee ◽  
Gordon R. Freeman
Keyword(s):  
Carbon Monoxide ◽  
Field Strength ◽  
Electric Field ◽  
Carbon Disulfide ◽  
Sharp Decrease ◽  
Liquid Carbon ◽  
Distance Distributions ◽  
Free Ion ◽  
Ion Yields ◽  
Liquid Carbon Disulfide

The electron ejected from a molecule by an energetic impact moves away from the resultant ion and loses energy to the molecules with which it collides. The distance such electrons travel away from their ions during thermalization can be estimated by measuring the free-ion yields as a function of electric-field strength. This was done in gaseous and liquid carbon disulfide and hexafluorobenzene over wide ranges of densities. The electron thermalization-distance distribution in C6F6 was the same as that in most other liquids; it was a Gaussian distribution with a power tail. However in liquid CS2 the distribution was different, an exponential with a power tail, as in liquid nitrogen and liquid carbon monoxide. The different distributions reflect differences in the thermalization processes. The thermalizing ability of both CS2 and C6F6 is less in the liquid than in the gas. There is an especially sharp decrease in the thermalizing ability of CS2 at the highest densities.

Piezoelectric Fields in Tilted GaInN Quantum Wells

2006 ◽  
Vol 955 ◽  
Author(s):  
Martin Feneberg ◽  
Frank Lipski ◽  
Rolf Sauer ◽  
Klaus Thonke ◽  
Thomas Wunderer ◽  
...  
Keyword(s):  
Field Strength ◽  
Quantum Wells ◽  
Electric Fields ◽  
Applied Voltage ◽  
Peak Shift ◽  
Total Field ◽  
Field Dependent ◽  
Piezoelectric Fields

ABSTRACTGaInN/GaN quantum wells (QWs) grown on different crystal facets have been investigated by field-dependent photoluminescence and electroluminescence experiments. Externally applied voltage changes the total field strength and direction of the electric fields inside the quantum wells, consisting of piezoelectric and built-in fields. Electroluminescence with increasing current results in a peak shift due to screening of the field by the injected carriers. By modeling the peak shifts of the photoluminescence (PL) and electroluminescence (EL) signals we found strong piezoelectric fields for a {0001} sample and nearly vanishing fields for a sample grown on the {1-101} plane of GaN.

Radiolysis Free Ion Yields and Electron Ranges in Polar and Nonpolar Liquids: Fluoromethanes

1973 ◽  
Vol 51 (7) ◽  
pp. 1010-1015 ◽  
Author(s):  
Maurice G. Robinson ◽  
Gordon R. Freeman
Keyword(s):  
Electric Field ◽  
Model Equation ◽  
Secondary Electrons ◽  
Applied Electric Field Strength ◽  
Electric Field Dependence ◽  
Free Ion ◽  
Nonpolar Liquids ◽  
Molecular Complexity ◽  
Ion Yields ◽  
Nonpolar Molecules

The free ion yields at zero applied electric field strength in the liquid fluoromethanes are Gfi0 in CH3F, 1.9 in CH2F2 and 1.1 in CHF3, all at 183 °K, and 0.07 in CF4 at 143 °K. Median ranges ymcd of the secondary electrons were estimated by fitting the electric field dependence of Gfi to a model equation: ymcd = 41 Å in CH3F, 39 Å in CH2F2 and CHF3, and 132 Å in CF4, at the above-mentioned temperatures. The average number of collisions, n, required to thermalize a secondary electron is about 64 000 in liquid Ar, 7 700 in CH4, 660 in C(CH3)4, 360 in CF4, 110 in C3H8, 44 in CH3F, 39 in CH2F2, 35 in CHF3, 17 in H2O, and 12 in CH3OH. The value of n with nonpolar molecules (up to neopentane in size) tends to decrease with increasing molecular complexity and with decreasing sphericity. Presence of a large dipole moment in the molecule decreases n further, and hydrogen bonds reduce n still more. Energy transfer between the electrons and rotational modes of the molecules appears to be important.

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