Search

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3+, CCl2+, CCl+, C+, Cl2+, and CCl32+ from CCl4; and for production of CCl2F+, CClF2+, CClF+, (CCl++CF2+), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2+,Cl+) and (CCl+,Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±5–7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch–Märk theory reproduces the experimental cross sections correctly for both targets. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3+, CCl2+, CCl+, C+, Cl2+, and CCl32+ from CCl4; and for production of CCl2F+, CClF2+, CClF+, (CCl++CF2+), Cl+, CF+, F+, and C+ from CCl2F2. Data are also reported for formation of (CCl2+,Cl+) and (CCl+,Cl+) ion pairs from CCl4. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ±5–7 %. The present partial cross sections for lighter fragment ions are found to be considerably greater than had been previously reported but the most recent total cross section measurements agree well with those reported here. Neither the binary-encounter-Bethe theory nor the Deutsch–Märk theory reproduces the experimental cross sections correctly for both targets. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of N[sub 2]O, H[sub 2]S, and CS[sub 2] are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of N[sub 2]O[sup +], N[sup +, sub 2], NO[sup +] , N[sup +], and O[sup +] from N[sub 2]O; for production of (H[sub 2]S[sup +] + HS[sup +] + S[sup +]) and H[sup +] from H2S; and for production of CS[sup +, sub 2], S[sup +, sub 2], CS[sup +], S[sup +], C[sup +], and CS²+[sub 2] from CS[sub 2]. The total cross sections are obtained as the sum of these partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly-charged ions is ±6 - 8 %. For all three targets the cross sections for production of lighter fragment ions are found to be greater than previously reported which is consistent with the presumption of incomplete collection of energetic ions in the earlier studies. Agreement with recent theoretical calculations is satisfactory for N[sub 2]O but not for H[sub 2]S or CS[sub 2]. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of methanol, ethanol, and 1-propanol are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in most of the absolute cross sections is ±6%-8%. Significant discrepancies are seen between the only prior methanol partial cross section determination and this study but the majority of published total cross section measurements and calculations are in good agreement with this work. [ABSTRACT FROM AUTHOR]

Absolute partial and total cross sections for electron-impact ionization of CH[SUB3]F, CH[SUB3]Cl, CH[SUB3]Br, and CH[SUB3]I are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for the production of CH[SUBn], F[SUP+], CH[SUBn]Cl[SUP+], CH[SUBn]Br[SUP+], CH[SUBn].I[SUP+], CH[SUP+,SUBn], F[SUP+], Cl[SUP+], Br[SUP+], I[SUP+], and H[SUP+], where n=0-3. Data are also reported for production of H[SUP+,SUB2], H[SUP+,SUB3], and doubly charged species at 100 eV. The total cross section for each target is obtained as the sum of the partial cross sections. The overall uncertainty in the absolute cross sections for most of the singly charged ions is ± 6%. It is observed that, although the Deutsch-Märk and the binary-encounter-Bethe theoretical formalisms are able to predict some features of the measured total cross sections, neither is consistently accurate. The simple ab initio method of Vallance et al. can apparently predict the value of the cross section maxima as well as the other more sophisticated approaches. [ABSTRACT FROM AUTHOR]

Absolute partial cross sections for electron-impact ionization of nitric oxide and nitrogen dioxide are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ions are collected irrespective of their initial kinetic energy. Data are presented for the production of NO[sup +], N[sup +], O[sup +], and NO[sup 2+] ions from NO; and for the production of NO[sub 2][sup +], NO[sup +], N[sup +], O[sup +], and (N[sup 2+]+O[sup 2+]) ions from NO[sub 2]. The overall uncertainty in the absolute cross section values is ±5% for singly charged parent ions, while that for the fragment ions may be as large as ±20%. For NO, the previously published data are generally in reasonable agreement with those presented here, although there remain some significant discrepancies with even the most recent work. No previous comprehensive study of NO[sub 2] has apparently been reported but the experimental NO[sub 2][sup +] cross section data that are available disagree substantially with the present measurements. The present total NO[sub 2] cross section is, however, in excellent agreement with recent theoretical work. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Absolute partial cross sections for the production of CO+2, CO+, CO2+2, O+, C+, O2+, and C2+ from electron-impact ionization of CO2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output provides clear evidence that all product ions are completely collected. The overall uncertainty in the absolute cross section values is ±3.5% for singly charged parent ions and is slightly greater for fragment and doubly charged ions. For the fragment ion cross sections, all but one of the previous measurements are observed to be significantly lower than the present results. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Collisions between atoms in high Rydberg states and molecules that dissociatively attach free low-energy electrons can lead to ionization through capture of the excited electron by the target molecule. A Monte Carlo code is described that models the detailed kinematics of such dissociative electron transfer reactions. The model takes into account the velocity distributions of the reactants, the lifetime and decay energetics of the transient intermediate negative ion, and the electrostatic interaction between the product positive and negative ions. Data for CF3I are presented that illustrate how detailed comparisons between model predictions and experimental data can lead to a better understanding of the dynamics of dissociative electron attachment reactions. In particular, such comparisons can provide estimates of the lifetime of the intermediate negative ions and show how the excess energy of reaction is partitioned between translational and internal degrees of freedom in the dissociation process. [ABSTRACT FROM AUTHOR]

The lifetimes of the transient negative ions formed during dissociative electron capture by CHCl3 and CCl4 have been investigated through studies of electron transfer in collisions with K(nd) Rydberg atoms. Measurements of the velocity and angular distributions of the product positive and negative ions reveal that transient CHCl-[ATOTHER]@B|[/ATOTHER]3 ions formed by Rydberg electron attachment to CHCl3 undergo very rapid dissociation. Similar data indicate that CCl-*4 ions formed through Rydberg electron capture by CCl4 have much longer lifetimes, on the order of 10 to 30 psec, consistent with the predictions of RRKM theory. [ABSTRACT FROM AUTHOR]

Negative ion production via electron transfer in collisions between K(nd) Rydberg atoms and CF3Br and CF2Br2 has been investigated over a wide range of of n (10≤n≤70). For both species, the major negative ion observed is Br-, although with CF2Br2, a small Br-2 signal is also detected. Kinematic studies show that Br- production via dissociative attachment is accompanied by sizable translational energy release (∼0.35 eV for CF3Br; ∼0.2 eV for CF2Br2). These studies further show that, despite this large energy release, post-attachment interactions between the product ions are important at intermediate values of n(n≾20) and suggest that the transient CF3Br-[ATOTHER]@B|[/ATOTHER]and CF2Br2-* ions initially formed by electron capture have quite different lifetimes against dissociation. Cross sections for free-electron attachment to both species are derived from measurements of rate constants for electron transfer at high n. These cross sections are in reasonable agreement with results obtained in free-electron studies using the threshold photoelectron spectroscopy technique. [ABSTRACT FROM AUTHOR]

A kinematic study of the velocities and angular distribution of I- ions detected following Rydberg electron transfer in K(nd)/CF3I collisions is reported. The data show that post-attachment interactions between the product ions are important at intermediate n (9<=n<=20) even though the I- ions are formed with appreciable kinetic energies. [ABSTRACT FROM AUTHOR]