Dissociative Excitation of Some Oxygen-Containing Molecules: Lifetimes and Electron-Impact Cross Sections
TL;DR: In this article, the lifetime of seven vacuum-ultraviolet O I and O II emission multiplets were measured using a pulsed electron beam in low-pressure samples of CO, NO, and ${\mathrm{H}}_{2}$O. The lifetimes and cascade patterns of the lines are consistent with known autoionization processes.
Abstract: Decay lifetimes of seven vacuum-ultraviolet O I and O II emission multiplets have been measured using a pulsed electron beam in low-pressure samples of ${\mathrm{O}}_{2}$, CO, NO, and ${\mathrm{H}}_{2}$O. The lifetimes and cascade patterns of the lines are consistent with known autoionization processes. In two cases, spin-orbit-induced autoionization rates are determined. Absolute electron excitation functions for 8447---\AA{} O I have been measured in the above gases. Relative excitation functions for 1304-\AA{} O I are normalized to the 8447-\AA{} absolute cross section by means of a time-domain cascade analysis. A method for computing relative cross sections from $N$-exponential decays is outlined.
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TL;DR: In this paper, the authors used two-photon laser-induced fluorescence to obtain quantitative measurements of the concentration of ground state O atoms in O2+CF4-rf discharges.
Abstract: We have used two‐photon laser‐induced fluorescence to obtain quantitative measurements of the concentration of ground state O atoms in O2+CF4 rf discharges. Absolute calibration was achieved by generating a known concentration of atomic oxygen by UV laser photolysis of O2. Trace amounts of Ar were added to serve as an inert reference gas for concurrent optical emission measurements, in which the plasma‐induced optical emission intensities from O* and Ar* lines were recorded. Emission line shapes were measured using a Fabry–Perot interfermoter to gain information on the mechanisms for formation of excited oxygen atoms in the plasma. Two excitation mechanisms were found to be important: (1) electron impact excitation of ground state atoms, e+O → O*+e, and (2) dissociative excitation of O2, e+O2 → O*+O+e. Evidence for both excitation mechanisms was obtained for O* (8446 A) emission, with atomic excitation being dominant, whereas dissociative excitation appeared to be the dominant mechanism for O* (7774 A) em...
237 citations
TL;DR: In this article, a wide range of oxygen-containing molecules following impact with electrons of carefully controlled energy is critically reviewed, ranging from diatomics, like O_2 and CO, to large molecules of biological and technological interest.
181 citations
TL;DR: In this paper, the analytical characterizations of electron impact cross sections for important atmospheric gases (namely, O2, N2, O, CO, CO2 and He) are updated.
Abstract: The analytic characterizations of electron impact cross sections for important atmospheric gases (namely, O2, N2, O, CO, CO2, and He) are updated. With these cross sections it is simple to communicate massive quantities of experimental and theoretical results. In addition, these forms are convenient for applications in energy degradation calculations, including a new approach described in a companion paper.
172 citations
TL;DR: In this article, the electron impact on CO2 has been used to produce vacuum ultraviolet multiplets of C I, C II, and O I. The dependence of the excitation functions on electron energy shows that these multiplets are produced by electric-dipole-allowed transitions in CO2.
Abstract: Vacuum ultraviolet multiplets of C I, C II, and O I were produced by electron impact on CO2. Absolute emission cross sections for these multiplets were measured from threshold to 350 eV. The electrostatically focused electron gun used is described in detail. The atomic multiplets which were produced by dissociative excitation of CO2 and the cross sections at 100 eV are presented. The dependence of the excitation functions on electron energy shows that these multiplets are produced by electric-dipole-allowed transitions in CO2.
143 citations
TL;DR: The measured lifetime of 39 (0) and 27 (N) nsec and quenching rate constants of 2.5 x 10(-10) cm(-3) sec(-1) for collisions of N(2) with each atom indicate promise for this method as a diagnostic tool in flames and plasmas.
Abstract: The 3p (3)P state of O and the 2s(2)2p(2)3p (4)D(0) states of N are populated by two-photon absorption at 226 and 211 nm, respectively, and the resulting near-IR fluorescence is detected. The exciting photons are provided by stimulated Raman frequency shifting, and the experiments are performed in a flow discharge. The measured lifetime of 39 (0) and 27 (N) nsec and quenching rate constants of 2.5 x 10(-10) cm(-3) sec(-1) for collisions of N(2) with each atom indicate promise for this method as a diagnostic tool in flames and plasmas.
127 citations
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TL;DR: In this article, a compilation and critical evaluation of absolute cross-sections for ionization of atoms and diatomic molecules by electron impact is presented, along with a brief discussion of relative cross-section data near threshold.
Abstract: This review includes a compilation and critical evaluation of absolute cross sections for ionization of atoms and diatomic molecules by electron impact. Experimental techniques used for ionization are surveyed. Selected relative cross sections for production of multiply charged ions and a brief discussion of relative cross-section data near threshold are presented. Absolute limits are not set on the size of probable systematic errors in the various experiments.
576 citations
TL;DR: An electrostatic lens system which compensates for chromatic aberration has been tested in an electron spectrometer and the results indicate that this lens is suitable for comparisons of peak intensities in electron impact spectra.
Abstract: An electrostatic lens system which compensates for chromatic aberration has been tested in an electron spectrometer. The results indicate that this lens is suitable for comparisons of peak intensities in electron‐impact spectra. Relative intensities in vibrational progressions that belong to a single electronic transition have been studied in N2, CO, and NH3 and found to be nearly independent of the scattering angle. Electron‐impact spectra have been reported for helium, nitrogen, oxygen, argon, nitric oxide, nitrous oxide, ammonia, water vapor, carbon dioxide, ethylene, acetylene, and benzene at electron kinetic energies between 33 and 100 eV. Spectral regions of special interest are encountered in CO2 and C6H6. At excitation energies of 7–10 eV in CO2 a change in intensity distribution, attributed to transition from an electric‐quadrupole to an electric‐dipole spectrum, is observed as the kinetic energy is raised. In the case of C6H6 a change in the spectrum with angle is encountered which strongly sugg...
410 citations
TL;DR: In this article, the radiative lifetimes of seventeen excited states in H2, N2, n2+, CO, CO+, CO+, NO, NO+, BF, CF, BCl, and CO2+ have been measured by the phase shift technique of Lawrence.
Abstract: The radiative lifetimes of seventeen excited states in H2, N2, N2+, CO, CO+, NO, NO+, BF, CF, BCl, and CO2+ have been measured by the phase‐shift technique of Lawrence. The measured lifetimes were derived from transitions in the 960‐4500‐A region and range from 0.6 nsec in H2 to 118 nsec in CO2+. Particular attention has been paid to the understanding and elimination of possible sources of systematic errors in the absolute phase shift measurements. The lifetimes have been combined with measured and calculated emission intensities to derive electric dipole transition moments and absorption oscillator strengths for the diatomic band systems.
295 citations
TL;DR: The experimental and theoretical literature about the electron impact excitation of atoms is reviewed in this paper, where the reliability of the various methods is discussed and a general critique of the optical method of measuring excitation functions is given, with the objective of promoting higher quality future experimental work.
Abstract: : The experimental and theoretical literature about the electron impact excitation of atoms is reviewed. Theoretical methods ranging from the Bethe and Born approximations to the close coupling approximations are discussed and intercompared. Where possible, on theoretical grounds or through intercomparison, the reliability of the various methods is discussed. A general critique of the optical method of measuring excitation functions is given, with the objective of promoting higher quality future experimental work. A critical study of existing experimental work leads to the conclusion that most workers have ignored important physical and instrumental effects, and it may be presumed that the data in the literature is subject to many unrecognized systematic errors. The literature on hydrogen and helium is discussed critically. The literature on the alkalis, heavy rare gases, mercury, cadmium and zinc is surveyed but the quality of the literature does not support critical review beyond some general comments about the physics of these atoms. (Author)
288 citations
TL;DR: In this article, it was shown that the degree of polarization is related to the form of the anistropy in the angular distribution of dissociation products, and that this form of anisotropic anisomorphism can be used to explain the anomalous behavior of molecular dissociative processes.
Abstract: Fluorescence from excited atomic fragments which arises from molecular dissociative processes can be shown in general to be polarized. The degree of polarization is related to the form of the anistropy in the angular distribution of dissociation products.
173 citations