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The dissociation of a wide range of oxygen-containing molecules following impact with electrons of carefully controlled energy is critically reviewed. Molecules considered range from diatomics, like O_2 and CO, to large molecules of biological and technological interest. Dissociation mechanisms are discussed and, where possible, quantitative data for the various possible processes, ionization, attachment, dissociation, excitation, emission etc., are presented. Gaps and discrepancies in our current data base are highlighted. Both graphical and tabular data are presented.

New measurements of differential cross-sections for excitation of the a″ 1Σ+g (v' = 0, 1) state in molecular nitrogen reveal a cusp-like angular distribution. This feature is distinctly observed for the first time in the present electron energy-loss experiment as a result of finer scattering angle grid and impact energy coverage than previous measurements. This feature is similar to that observed in atomic targets such as He, Hg and Ba. The observed phenomenon suggests an interference effect related to configuration–interaction coupling between lower and excited states that are of the same symmetry. It is hoped that the present work will stimulate theoretical investigations into the physics that governs this cusp-like behaviour.

In 1990, two significant reviews of electron–atomic-oxygen collision processes were published. Since that time, a large volume of both experimental and theoretical research into these processes has occurred. These data are reviewed and recommendations regarding existing data sets and future research in this area are made. Attention is given to the challenges associated with handling atomic oxygen in terms of both experiment and theory. PACS Nos.: 34.80.Bm, 34.80.Dp

New electron-impact differential cross-section (DCS) and DCS ratio measurements for the excitation of the four levels making up the 3p54s configuration of argon are reported at incident electron energies of 14, 15, 17.5, 20, 30, 50 and 100 eV. These cross-sections were obtained using a conventional high resolution electron spectrometer. Elastic electron scattering from argon was used as a calibration standard. Electron–helium DCSs were used to determine the instrumental transmission of the spectrometer. Further checks of the relative shape of these DCS measurements were made using the method of gas mixtures (Ne mixed with Ar). We also present results from new calculations of these DCSs using the R-matrix method, the unitarized first-order many-body theory, the semi-relativistic distorted-wave Born approximation, and the relativistic distorted-wave method. Comparison with available experimental DCSs and DCS ratios is also presented.

Differential and integral cross sections (ICSs) for excitation in atomic oxygen have been measured at electron-impact energies of 15, 17.5, 20, 22.5 and 27.5 eV. Differential measurements were conducted with a conventional electron energy-loss spectrometer and a microwave discharge source of atomic oxygen. Relative differential cross sections (DCSs) were determined between 15 and 30 eV impact energy. With the help of theoretical predictions of the shape of the DCS at large angles, measured results were extrapolated to 180° scattering angle and relative ICSs were deduced. The relative excitation function was normalized to the 30 eV impact energy ICS given by Kanik et al (2001 J. Phys. B: At. Mol. Opt. Phys. 34 2647). Normalization of the ICS values allowed the measured DCSs to be put on the absolute scale. Theoretical calculations of the DCSs were carried out using the R-matrix with the pseudostates approach. A total of 22 spectroscopic bound and autoionizing states, together with 19 pseudostates, were included in the close-coupling expansion. The pseudostates were chosen to simulate continuum target states. Theoretical results, along with other available experimental data, have been compared with the current experimental results.

We report electron-impact-induced emission cross sections for the 2p4 3P–3s 3So (130.4 nm), 2p4 3P–3d 3Do (102.7 nm), 2p4 3P–3s' 3Do (98.9 nm) and 2p4 3P–3s'' 3Po (87.8 nm) transitions of atomic oxygen. Measurements were made using a magnetically confined electron beam in collision with atomic oxygen produced by an extended microwave discharge source in a crossed-beam arrangement. A 0.2 m vacuum ultraviolet diffraction spectrometer was used to record the emission. The absolute excitation functions of these transitions were determined by normalizing to the O I (130.4 nm) cross section produced by dissociative excitation of O2 at 100 eV impact energy (Noren et al 2001a Geophys. Res. Lett. 28 1379). A 60-state model of the O I electron reaction structure has been used to extract the excitation cross sections from the experimental measurements. The model process establishes analytic collision strengths to the asymptotic limit.

We report absolute differential electron scattering cross sections (DCSs) of molecular oxygen (O2) at 20, 30, 50 and 100 eV impact energies (E0). DCSs were measured for inelastic features in the 6.5-12.5 energy-loss range including the Schumann-Runge (SR) continuum, the longest band (LB) and the second band (2B) along with the summed DCS for the third band (3B) plus the 10.76 and 11.03 eV energy-loss features. Measurements were performed at scattering angles of 0°, 5°, 10°, 15°, 20° and 25° using a conventional electrostatic electron energy-loss spectrometer. Inelastic electron energy-loss spectra of O2 were measured giving relative inelastic DCSs, which were then normalized via the relative flow technique using inelastic He and Ne transitions as standards. Past works (Trajmar et al 1972, Shyn et al 1994) have shown good relative agreement while displaying significant discrepancies in absolute terms. The current normalization technique represents an improvement over those employed in previous inelastic O2 DCS work. As such, the present results serve to firmly establish the absolute normalization of these DCSs. Furthermore, the current results are able to provide an additional test of the relative angular distributions of previous works throughout the important low-angle region where the DCSs undergo the most rapid change. This paper also represents the first measurements of inelastic O2 DCSs to extend right down to the forward-scattering limit.

We report both experimental and theoretical differential and integral excitation cross sections of atomic oxygen corresponding to the 2s22p4 3P→3s 3S (130.4 nm), 2s22p4 3P→3d 3D (102.7 nm), 2s22p4 3P→3s' 3D (98.9 nm) and 2s22p4 3P→3s'' 3P (87.8 nm) transitions at 30, 50, and 100 eV electron-impact energies. Experimental measurements have been made in the angular range from 0° to 25° with a conventional electrostatic electron energy-loss spectrometer. The atomic O differential cross sections (DCSs) were put on an absolute scale by normalization to the O2 DCS values of Johnson and Kanik (2001). Extrapolation of the measured results to larger angles was performed using theoretical calculations as a guide, and integral cross sections were derived. Theoretical calculations based on the R-matrix method, along with other available experimental data, have been compared with the current experimental results.

The optical excitation function of the O I 3So→ 3P transition (130.4 nm), produced by electron-impact excitation of atomic oxygen, has been measured over an extended energy range from threshold to 1.0 keV. Measurements were obtained in a crossed-beam experiment using both magnetically confined and electrostatically focused electrons in collision with atomic oxygen produced by a microwave discharge source. A 0.2 m vacuum ultraviolet monochromator system was used to measure the emitted O I radiation at 130.4 nm. The relative O I (130.4 nm) emission intensity corresponding to the 3So→ 3P transition was then put on the absolute scale by normalization to the O I (130.4 nm) cross section produced by dissociative excitation of O2 at 30 eV (Kanik et al 2000).

This paper is the second part of two back-to-back papers concerning electron-impact excitation of Kr. This part concerns excitation of the individual levels that constitute the 4p55p, 4p54d and 4p56s configurations of Kr, at incident electron energies (E0) of 20.0 and 15.0 eV, for scattering angles (θ) ranging from 10° to 130°. As in part I, excitation cross sections are measured and calculated using the R-matrix (RM) and the unitarized first-order many-body theory (UFOMBT) methods. Comparisons between the present experimental and theoretical results, and also with other experimental results, are presented.

We have measured the differential and integral cross sections for electron impact excitation of the , , and states of CO in the 10-15 eV impact energy region. These measurements fill the gap which existed between the low-energy (threshold to about 12 eV) data of Zobel et al and the intermediate energy (20-50 eV) results of Middleton et al. Recent electron time-of-flight measurements are utilized to place the relative cross sections (deduced from energy-loss spectra) on the absolute scale. The cross sections are in excellent agreement with the results obtained by Zobel et al at the overlapping impact energies and always smoothly extrapolate to their low-energy results. Extrapolation to the intermediate energy domain and comparison with the results of Middleton et al is not so clear. Comparison with theoretical differential and integral cross sections of Sun et al and the integral cross sections of Morgan and Tennyson reveals angular and energy dependences which resemble those found for the experimental results but there are serious discrepances concerning the absolute magnitudes.

The optical excitation function of prompt Lyman-\ensuremath{\alpha} radiation, produced by electron impact on atomic hydrogen, has been measured over the extended energy range from threshold to 1.8 keV. Measurements were obtained in a crossed-beams experiment using both magnetically confined and electrostatically focused electrons in collision with atomic hydrogen produced by an intense discharge source. A vacuum-ultraviolet monochromator system was used to measure the emitted Lyman-\ensuremath{\alpha} radiation. The absolute H(1s-2p) electron impact excitation cross section was obtained from the experimental optical excitation function by normalizing to the accepted optical oscillator strength, with corrections for polarization and cascade. Our data are significantly different from the earlier experimental results of R. L. Long et al., J. Res. Natl. Bur. Stand. Sect. A 72A, 521 (1968) and J. F. Williams, J. Phys. B 9, 1519 (1976); 14, 1197 (1981), which are limited to energies below 200 eV. Statistical and known systematic uncertainties in our data range from \ifmmode\pm\else\textpm\fi{}4% near threshold to \ifmmode\pm\else\textpm\fi{}2% at 1.8 keV. Multistate coupling affecting the shape of the excitation function up to 1 keV impact energy is apparent in both the present experimental data and present theoretical results obtained with convergent close-coupling (CCC) theory. This shape function effect leads to an uncertainty in absolute cross sections at the 10% level in the analysis of the experimental data. The derived optimized absolute cross sections are within 7% of the CCC calculations over the 14 eV--1.8 keV range. The present CCC calculations converge on the Bethe-Fano profile for H(1s-2p) excitation at high energy. For this reason agreement with the CCC values to within 3% is achieved in a nonoptimal normalization of the experimental data to the Bethe-Fano profile. The fundamental H(1s-2p) electron impact cross section is thereby determined to an unprecedented accuracy over the 14 eV -- 1.8 keV energy range.

Experimental and theoretical differential cross sections (DCSs) for electron impact excitation of the five lowest levels of xenon are reported. The experimental data were obtained at impact energies of 10, 15, 20 and 30 eV for scattering angles in the range of to . The scattering intensities for excitation of various levels with respect to that of the combined two lowest levels (representing the corresponding DCS ratios) were measured with conventional electrostatic electron energy-loss spectrometers. Absolute DCSs for excitation of the combined two lowest levels were derived from DCS ratios for excitation of the combined two lowest levels and elastic scattering and utilizing the elastic DCSs of Register et al. These DCS ratios were obtained from scattering intensity ratios measured with conventional electrostatic electron energy-loss spectrometers after correction for instrumental effects by utilizing electron time-of-flight measurements for determining the proper value of this ratio at scattering angle for each impact energy. The unitarized first-order many-body theory and the unitarized distorted-wave approximation were applied to obtain the theoretical differential cross sections for impact energies of 10, 15, 20, 30, 50 and 80 eV. The present experimental and theoretical results are compared with each other and with other available experimental and theoretical DCSs.

The next generation of high resolution UV imaging spacecraft are being prepared for studying the airglow and aurora of the Earth, the other terrestrial planets and the Jovian planets. To keep pace with these technological improvements we have developed a laboratory program to provide electron impact collision cross sections of the major molecular planetary gases (H2, N2, CO2, O2, and CO). Spectra under optically thin conditions have been measured with a high resolution (lambda/delta(lambda) = 50000) UV spectrometer in tandem with electron impact collision chamber. High resolution spectra of the Lyman and Wemer band systems of H2 have been obtained and modeled. Synthetic spectral intensities based on the J-dependent transition probabilities that include ro-vibronic perturbations are in very good agreement with experimental intensities. The kinetic energy distribution of H(2p,3p) atoms resulting from electron impact dissociation of H2 has been measured. The distribution is based on the first measurement of the H Lyman-alpha (H L(alpha)) and H Lyman-beta (H L(beta)) emission line Doppler profiles. Electron impact dissociation of H2 is believed to be one of the major mechanisms leading to the observed wide profile of H L-alpha from Jupiter aurora by the Hubble Space Telescope (HST). Analysis of the deconvolved line profile of H L-alpha reveals the existence of a narrow line peak (40 mA FWHM) and a broad pedestal base (240 mA FWHM). The band strengths of the electron excited N2 (C(sup 3) Pi(sub(upsilon) - B(sup 3)Pi(sub g)) second positive system have been measured in the middle ultraviolet. We report a quantitative measurement of the predissociation fraction 0.15 +/- 01(sup .045, sub .01) at 300 K in the N2 c'(sub )4 (1)sigma(sup +, sub g) - x(1)sigma(sup +, sub g)(00) band, with an experimental determination of rotational line strengths to be used to understand N2 EUV emission from Titan, Triton and the Earth.

The phenomenon whereby features associated with certain vibrational levels in molecular states of mixed electronic character disappear under specific scattering conditions in electron energy-loss spectra is investigated. In particular, using a combination of experimental measurements and coupled-channel calculations, anomalous vibrational intensities in the mixed valence-Rydberg ${}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}\ensuremath{\leftarrow}X\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Sigma}}_{g}^{+}$ transition of N${}_{2}$ are explained. A single parameter, i.e., the ratio of the generalized electronic transition moments to the diabatic valence and Rydberg components of the mixed states, dependent on the experimental scattering conditions, is found to be essentially capable of describing all observed relative vibrational intensities, including the near disappearance of the $b\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{}^{1}\phantom{\rule{-0.16em}{0ex}}{\ensuremath{\Pi}}_{u}(v=5)$ feature for momentum-transfer-squared values ${K}^{2}\ensuremath{\approx}0.3$ a.u. This result highlights the interesting possibility of experimental control of molecular quantum-interference effects in electron energy-loss spectra, something that is not possible in optical spectra.

Electron-impact excitation of CO plays an important role in planetary atmospheres and interstellar clouds. At the present time, serious discrepancies exist among excitation cross sections reported in the literature for this molecule. We measured electron-impact excitation cross sections for B 1 Σ + ← X 1 Σ + , C 1 Σ + ← X 1 Σ + and E 1 Π ← X 1 Σ + states of CO at 100 eV impact energy using electron energy-loss spectroscopy.

In this first part of a laboratory study of predissociation in CO the authors have measured in the electron-impact-induced fluorescence spectrum of CO in the wavelength range 40-125 nm at a spectral resolution of 0.5 nm. The experiment was performed in a crossed-beam configuration under optically thin conditions. Their spectral measurements at 200 eV electron impact, energy provide the emission cross sections of atomic dissociation fragments (C I, C II, O I, O II) and the vibrational transitions of the B 1 Sigma +, C 1 Sigma +, E 1 Pi -X 1 Sigma + band systems of CO. The measured emission cross sections of these molecular transitions will be needed for comparison with excitation cross sections from electron energy-loss spectra to determine predissociation yields.

[1] Vacuum ultraviolet emissions resulting from electron impact on O2 have been studied at 100, 200, and 300 eV. The ratio of the 83.4 nm and 130.4 nm emissions were used in combination with the recently revised recommendation of the O I (130.4 nm) cross section to determine the O II (83.4 nm) cross sections. The present results are compared with existing measurements and resolve the controversy that has existed regarding the magnitude and shape of the 83.4 nm emission cross section. We recommend an O II (83.4 nm) emission cross section of (1.50 ± 0.17) × 10−18 cm2 at 100 eV.

[1] The emission properties of the N2c′41Σu+ − X1Σg+ band system have been investigated in a joint experimental and coupled-channels theoretical study. Relative intensities of the c′41Σu+(0) − X1Σg+(vi) transitions, measured via electron-impact-induced emission spectroscopy, are combined with a coupled-channel Schrodinger equation (CSE) model of the N2 molecule, enabling determination of the diabatic electronic transition moment for the c′41Σu+ − X1Σg+ system as a function of internuclear distance. The CSE rotational transition probabilities are further verified by comparison with a high-resolution experimental spectrum. Spontaneous transition probabilities of the c′41Σu+ − X1Σg+ band system, required for modeling atmospheric emission, can now be calculated reliably.

The results of an investigation concerning the sensitivity of conventional unfolding methods applied to electronic-vibrational electron-energy-loss spectra to the transmission efficiency of electron spectrometers are presented. This investigation was made in an effort to understand differences in the differential cross sections for excitation of low-lying electronic states determined experimentally by various groups using electronic-vibrational energy-loss spectra of ${\mathrm{N}}_{2}$. In these experiments, very similar spectral unfolding methods were used, which relied on similar Franck-Condon factors. However, the overall analyses of the electron scattering spectra (by the individual groups) resulted in large differences among the differential cross sections determined from these energy-loss spectra. The transmission response of the experimental apparatus to different-energy scattered electrons has often been discussed as a key factor that caused these disagreements. The present investigation shows in contrast that the effect of transmission is smaller than that required to independently explain such differences, implying that other systematic effects are responsible for the existing differences between measurements.

[1] Integral cross sections for electron impact excitation out of the ground state (X 1Σg+) to the A 3Σu+, B 3Πg, W 3Δu, B′ 3Σu−, a′ 1Σu−, a 1Πg, w 1Δu, and C 3Πu states in N2 are reported at incident energies ranging between 10 and 100 eV. These data have been derived by integrating differential cross sections previously reported by this group. New differential cross section measurements for the a 1Πg state at 200 eV are also presented to extend the range of the reported integral cross sections for this state, which is responsible for the emissions of the Lyman-Birge-Hopfield band system (a 1Πg → X 1Σg+). The present results are compared and critically evaluated against existing cross sections. In general, the present cross sections are smaller than previous results at low impact energies from threshold through the excitation function peak regions. These lower cross sections have potentially significant implications on our understanding of UV emissions in the atmospheres of Earth and Titan.

[1] The kinetic energy distribution of oxygen atoms resulting from electron impact dissociation of O2 has been measured. A high-resolution vacuum ultraviolet spectrometer was employed for the measurement of the OI(115.2 nm, 130.4 nm, 135.6 nm) fine-structure emission line profiles at 35 eV and 100 eV electron impact energies. The deconvolved line profiles of atomic oxygen reveal the existence of a broad line profile (∼30–40 mA full width at half maximum) produced from a combination of dissociative excitation and dissociative ionization excitation processes. The atomic oxygen kinetic energy distributions at 100 eV electron impact energy spans the energy range from 1 to 10 eV, with a peak value near 1 eV. The excitation functions of OI(115.2 nm, 130.4 nm, 135.6 nm) were measured in the vicinity of threshold, from 14 to 50 eV. The PACS classification is 34.80.Gs (electron scattering-molecular dissociation) and 33.50Dq (molecular spectra-fluorescence).

[1] In this work, we report the OI(135.6 nm) absolute emission cross section resulting from the long-lived (180 μs) OI(5S → 3P) transition from dissociative excitation of O2. From the ratio of the integrated intensities of the OI(135.6 nm) and OI(130.4 nm) features and from the absolute emission cross section for the OI(130.4 nm) emission feature from electron impact dissociative excitation of O2 at 100 eV, the absolute emission cross section for the OI(135.6 nm) feature was determined to be 6.4 × 10−18 cm2 at 100 eV. Electron impact-induced optical excitation functions for optically allowed transitions at 115.2 nm and 130.4 nm and for an optically forbidden transition at 135.6 nm were also obtained over the electron impact energy range 0–600 eV. The OI(135.6 nm) emission cross section was measured in the laboratory utilizing a large collision chamber (1.5 m in diameter). Electrons were produced with an electrostatically focusing gun with a large focal length (50 cm). The OI(130.4 nm, 135.6 nm) excitation functions were put on an absolute scale as described in the text, and the OI(135.6 nm)/OI(130.4 nm) ratio was determined for the entire energy range (0–600 eV). The atomic O UV emission cross sections from dissociative excitation of O2 can be used to model the recent Hubble Space Telescope observations of OI(130.4 nm) and OI(135.6 nm) intensities from Ganymede [Feldman et al., 2000] and Europa [Hall et al., 1995, 1998].

We have used the convergent close-coupling method and a unitarized first-order many-body theory to calculate integral cross sections for elastic scattering and momentum transfer, for excitation of the 5d^2 ^1S, 6s6p^1P_1, 6s7p^1P_1, 6s8p^1P_1, 6s5d^1D_2, 5d^2^1D_2, 6s6d^1D_2, 6p5d^1F_3, 6s4f^1F_3, 6p5d^1D_2, 6s6p^3P_{0,1,2}, 6s5d^3D_{1,2,3}, and 6p5d^3D_2 states, for ionization and for total scattering by electron impact on the ground state of barium at incident electron energies from 1 to 1000 eV. These results and all available experimental data have been combined to produce a recommended set of integral cross sections., Comment: 47 pages, 8 tables, 25 figures

The integral cross sections (ICSs) for the electron impact excitation of the 3P-1D transition in atomic oxygen calculated by Plummer et al. (J. Phys. B, 37, 2979 (2004)) were incorrectly represented in Fig. 3. An error was made calibrating the impact energy axis (i.e., the x axis) while digitizing the curve from the original publication. The corrected figure is, therefore, provided. Further, the “continuous line” in Fig. 3 was incorrectly labelled in the caption as “Zatsarinny (26-state approximation)” when it should have read “Zatsarinny and Tayal (26-state approximation).” The corrected figure does not impact any of the discussion provided in the original paper. However, one should note that, as seen in the corrected figure, the Plummer et al. (J. Phys. B, 37, 2979 (2004)) calculation of the 3P–1D transition is in near perfect agreement with that of Zatsarinny and Tayal (J. Phys. B, 34, 1299 (2001)) as is the case for the 3P–1S transition shown in Fig. 4. (See next page for figure.)

Electron-atom (molecule) collision physics is concerned with the many processes (elastic scattering, momentum transfer, excitation, ionization, dissociation, etc.) that can take place as a result of such collisions. Instrumentation and experimental techniques for such studies have improved significantly in recent years, allowing more accurate electron collision measurements to be carried out. This progress has been motivated by the need for electron collision data for a variety of reasons, ranging from understanding the fundamental nature of the interactions to modeling the behavior of several physical systems (various discharge and laser systems, fusion plasmas) and environments (astrophysical plasmas, ionospheric and auroral processes of planetary atmospheres). At the same time, a great deal of progress has also been made in the theoretical area of collision physics, and the interplay between theory and experiments has further enhanced developments in this field.

Photodissociation cross sections and oscillator strengths for H2 from the X?1?+g (vi, Ji) levels to the continuum levels of the B?1?+u, C?1?u, B, D'?1?u and 5p??1?+u states have been calculated. The (vi, Ji) state-specific electron impact dissociation cross sections to the continuum levels of these states have been obtained for the first time over a wide energy range using calculated continuum oscillator strengths along with previously published excitation functions of the Lyman and Werner bands. Estimated cross sections to the higher (n ? 5) np??1?+u and np??1?u continua are also provided. Both photon and electron impact excitation cross sections show strong dependences on the initial (vi, Ji) quantum numbers. Thermally averaged electron impact cross sections of all singlet ungerade states increase monotonically with temperature. While excitation to the B'?1?+u continuum is the dominant dissociation channel at room temperature, the C?1?u and B?1?+u continua become more important at high temperature (>5000 K). This work, along with the previous calculation of the B'?1?+u and D?1?u states by Liu et al (2009a J. Phys. B: At. Mol. Opt. Phys. 42 185203), provides the complete electron impact dissociation cross section of H2 through the singlet ungerade continua. Electron dissociation cross sections of the singlet ungerade continua are provided for the purpose of modelling atmospheric heating, analysis of occultation measurements and the hot atomic hydrogen plume observed at Saturn.

Electron collisions with N2 are predominant components of the interaction between outer solar-system atmospheres and solar photons, solar wind, and magnetospheric electrons. Our collaboration between the Jet Propulsion Laboratory (JPL) and the California State University, Fullerton (CSUF), has devoted a significant effort over the last few years to improving the knowledge base of electron-N2 excitation phenomena. Here, we highlight the lack of Franck-Condon behaviour in excitation of the Rydberg-valence states, using excitation of the C 3Πu state as a case in point. Further, we briefly introduce ongoing work measuring vibrationally-resolved emission cross sections for the Lyman-Birge-Hopfield (LBH) band system of the a 1Πg (v') → X 1Σ+g (v'') transitions. Specifically, we present preliminary results for the relative (3,0) emission cross section, which calls the currently accepted LBH shape function of Ajello and Shemansky (1985 J. Geophys. Res.-Space 90 9845) into question.

Rotational and vibrational dependence of photodissociation cross sections and oscillator strengths to the continuum levels of the H and states have been examined. The electron-impact excitation, dissociation and emission cross sections of the and band systems have been obtained for the first time over a wide energy range by using calculated continuum oscillator strengths along with previously published discrete transition probabilities and Lyman and Werner bands excitation functions. The present photodissociation cross section from the Ji = 0 level is in excellent agreement with that obtained by Glass-Maujean (1986 Phys. Rev. A 33 346–50). Photoexcitation from the state to the continuum is found to be weak. The present calculation shows significant contribution of quasi-resonance, which arises from transitions to the quasi-bound levels above the dissociation limit but stabilized by the centrifugal potential. The quasi-resonance is largely responsible for the significant rotational dependence of the continuum oscillator strength of the transition, which, in turn, leads to the noticeable temperature dependence of electron-impact excitation and emission cross sections. and electron-impact excitation, emission, and dissociation cross sections, important for modelling dayglow and auroral activity in the atmospheres of the outer planets, are presented.

Vacuum ultraviolet emissions following electron impact dissociative excitation of N2O have been studied over the wavelength range 80–180 nm and for electron energies from threshold up to 300 eV. Calibrated spectral data are presented at 100 eV incident energy. The dominant N I (2p3 4S°–3s 4P) multiplet at 120.0 nm has a measured maximum cross section of (2.2 ± 0.4) × 10−18 cm2 at 100 eV, which in turn was used to normalize 100 eV cross sections for all observed spectral features. In addition, excitation functions corresponding to the dominant emission features have been analysed in detail with particular emphasis on the near-threshold region. Possible dissociation channels are discussed.

Collisions between electrons and neutral species play an important role in the energy balance of upper atmospheres throughout the Solar System. These processes, and the subsequent photon emissions produced, provide one of the primary means for probing, diagnosing and understanding the dynamics of these environments. Modelling of these plasmas and interpretation of optical observations requires accurate knowledge of atomic/molecular parameters such as oscillator strengths and predissociation yields along with cross sections for electron impact excitation (and emission) with the constituent species of these atmospheres. In this paper, our recent work involving electron collisions with two of the most important atmospheric species in our Solar System, namely N2 and H2, will be reviewed. Preliminary differential cross sections for excitation of the B 1Σ+u and C 1Πu states out of the X 1Σg+(v'' = 1) ground state level of H2 are presented.

Measurements of the middle ultraviolet (MUV) electron impact induced fluorescence spectrum of SO2 from 200 to 430 nm in a crossed beam experiment are reported. The spectrum is dominated by two features at the experimental resolution of 0.5 nm; these two features are referred to as MUV1 and MUV2. MUV1 is the SO band system extending from 240 to 265 nm produced by dissociative excitation. MUV2 is a blend of the SO2 and SO2(+) molecular band systems in the range 264-430 nm. The excitation function measurements of MUV2 indicate that low-energy electrons effectively prepare SO2 in one or more electronically excited triplet states that involve the SO2 state by direct excitation and/or cascading. The peak cross section for MUV1 occurs at 20 eV with a value of 25.0 +/-5.5 x 10 exp -19 sq cm. The peak cross section for MUV2 arises at 9 eV with a value of 368 +/-81 x 10 exp -19 sq cm. The laboratory results provide a plausible explanation of the Io auroral hot spots observed by Voyager 2.