Search

This dissertation investigates assessment development in urban on land surface temperature using geospatial technique with land use land cover and variation between 1986 and 2016. The aim of this study is to examine the effect of urbanization on land surface temperature using GIS and Remote Sensing technique. Satellite images used for this dissertation were Thematic Mapper ™ acquired on 1986, Enhance Thematic Mapper plus (ETM+) acquired on 2001 and Operational Land Imager (OLI) acquired on 2016. All satellite data have 30-meter resolutions, Thematic Mapper and Enhance Thematic Mapper plus images have spectral range of 0.45 to 2.35 micro meters (µm) with 8 bands, while the Operational Land Imager extends to band 12. The images were used to produce land use/land cover map of Abuja Municipal Area Council (AMAC) for effective analysis of land surface temperature for three epochs to know the feature contributes most to surface temperature and changes over time. Results of land use/land cover shown that there is significant increment of Built-up from 36.74 per square kilometer to 283.7 per square kilometer between 1986 and 2016, water body from 1.21 to 1.32 per square kilometer and bare surface from 571.5 to 607.5 per square kilometer. There is also sharp decrement in vegetation from 714.4 to 452.34 per square kilometer and rock outcrop from 132.52 to 111.48 between 1986 and 2016. There is little rise in surface temperature from 1986 to 2016. Temperature rise from 15 to 26 degree Celsius (0C), built up, contributed most to surface temperature.

Land degradation and Desertification (LDD) are critical issues facing most states in northern Nigeria, with severe consequences for national food security. Land degradation refers to total loss of the productive capacity of the soils for present and future use while desertification is seen as a process whereby the productivity of arid or semi-arid land falls by 10% or more. The Environmental Sensitivity to Desertification Index (ESDI) is the most frequently applied indicator-based system for accessing Land Degradation and Desertification. The research reported here adopted the MEDALUS (Mediterranean Desertification and Land Use) approach for identifying environmentally sensitive areas (ESA) to desertification in Katsina State, Nigeria based on Soil Quality Index (SQI), Climate Quality Index (CQI) and Vegetation Quality Index (VQI). The findings from each of these indicators show the variability between the northern and southern parts of Katsina State. The northern part of Katsina state was found to be the most vulnerable area to desertification and is covered by soil having the highest sand depth while the southern part of the state was found to be the least affected by desertification. This result specifically highlights areas in the State that requires urgent attention and remediation. Findings from this research can be used to support informed decision-making and policy development to focus on sustaining the environment, as well as the livelihood of the communities in the affected local government areas in the northern part of the State, given the high sensitivity of the area to desert conditions.

At high resolving power -->(?/? ? ? 10,000) , we have measured the electron impact-induced fluorescence spectrum of H2 from 3300-10000 ? at 20 and 100 eV. We have analyzed the visible-optical-near-IR (VOIR) emission spectrum under optically thin, single-scattering experimental conditions. The high-resolution spectrum contains transitions from the gerade Rydberg series of singlet states to the ungerade series of Rydberg states ( -->EF1?g+, -->GK1?g+, --> H1?g+, -->I1?g, -->J1?g... ? B1?u+, -->C1?u, -->B'1?u+, -->D1?u) and the Rydberg series of triplet states dominated by -->d3?u, -->k3?u, -->j3?g? a3?g+ band systems. A model VOIR spectrum of H2 from 7500 to 10000 ?, based on newly calculated transition probabilities and line positions including rovibrational coupling for singlet gerade states, is in excellent agreement with the observed intensities. The rotational line emission cross sections for direct excitation of the singlet states at 100 eV and triplet states at 20 eV were measured. The absolute cross section values for excitation to the singlet gerade states at 100 eV was measured to be -->(4.58 ? 1.37) ? 10?18 cm2; the excitation cross section to the triplet states at 20 eV was found to be -->(1.38 ? 0.41) ? 10?18 cm2. The singlet gerade emission cross sections are the cascading cross sections to the UV spectrum (including the Lyman and Werner band systems) and the triplet state emission cross sections are the cascade dissociation cross sections of the H2 -->(a3?g+?b3?u+) continuum for the production of fast hydrogen atoms. Electrons are also effective in exciting high vibrational levels belonging to ungerade symmetry (B, B', C, D) which subsequently emit toward gerade symmetry states in the VOIR domain. Strong emission from the ungerade-gerade transitions are observed from 7300 to 7400 ?.

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).

Electron-impact-induced emission spectra of Xe corresponding to the resonance transitions in the FUV spectral region from 114-165 nm at 15, 20 and 30 eV impact energies are reported. Absolute emission cross sections corresponding to the Xe I spectral features at 15, 20 and 30 eV impact energies and optical excitation functions for the two most prominent transitions at 119.2 and 147.0 nm in the 0-100 eV energy range were measured. In addition, the integral cross sections for direct electron-impact excitation of the corresponding levels in Xe, obtained by integration of the differential cross section measurements of Khakoo et al (Khakoo M A et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3455, Khakoo M A et al 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3477) are compared with the present results and the theoretical calculations of Csanak (Csanak G 1996 Private communication). A comparison of the measured emission and integrated direct excitation cross sections is made leading to indirect estimation of the cascade contributions to the emission cross sections.

A high-resolution (Δλ ~ 95 and 240 mA, FWHM) electron-impact-induced emission spectrum of molecular hydrogen has been obtained in the wavelength range 760-900 A. Analysis of the spectrum results in the assignment of some previously unobserved as well as observed but unassigned emission lines. Emissions observed in the 760-900 A range and a few selected regions above 900 A at room temperature (300 K) are tabulated, together with their spectral assignments. The tabulation can be considered as a supplement to the H2 atlas of Roncin & Launay and can be used for the analysis of EUV emission spectra observed in the interstellar medium and planetary atmospheres where H2 is the major constituent. Emission, predissociation, and autoionization yields for some transitions below 800 A are discussed. A Δv ≠ 0 perturbation between the Jj = 2 levels for vj = 5 of the D' 1Π state and vj = 2 of the 10pπ 1Π state is inferred.

Excitation functions of the H2 Lyman (Ly) ( B1∑∑u - X1∑∑g) and Werner (W) (C1∏u - X1∑∑g ) band systems have been reanalyzed using a combination of measurements and theoretical considerations. These systems are prominent emitters in outer planet atmospheric dayglow and auroral activity and can be used to infer energy deposition and heating rates. Earlier measurements of the cross sections reported by Shemansky et al. [1985a] have been found to be inaccurate in the threshold energy region. A combination of high-resolution spectral and shape function measurements obtained at the Jet Propulsion Laboratory (JPL) in low- and medium-energy regions have been used to obtain relative excitation shape functions of the two systems. At energies above 250 eV, we have used the measurements obtained earlier by De Heer and Carriere [1971] in order to define the first two terms of the Born electric dipole collision strength. The complete set of collision strength terms is obtained by combining the JPL and De Heer and Carriere [1971] data. We have found that, contrary to results of Shemansky et al. [1985a], the shape functions of the H2 Ly and W systems, expressed in units of threshold energy, are the same within experimental error. Absolute cross sections of the H2 Ly and W systems are established using the theoretical oscillator strengths of Abgrall et al. [1987, 1993a, b, c] and Abgrall and Roueff [1989]. The atomic hydrogen H Ly α emission cross section resulting from dissociative excitation of H2 at 100 eV obtained from relative intensities of H2 W emission lines is also derived and compared with other experimental measurements. At a gas temperature of 300 K and electron energy of 100 eV, the cross sections for the H Ly α, H2 Ly, and W emissions are (0.716 ± 0.095) × 10−17, (2.62 ± 0.34) × 10−17, and (2.41 ± 0.31) × 10−17 cm2, respectively. The accuracy of the absolute values and shape functions is limited primarily by electron gun performance, as was the case for Shemansky et al. The rotational dependence of the transition dipole matrix elements and perturbations between the B 1∑+u and C1∏+u states have a significant effect on the cross sections.

The electron-impact-induced emission spectrum of H2 has been measured in the extended wavelength region 175-530 mm at a spectral resolution of 1.7 mm (FWHM). The laboratory spectra are characterized by underlying H2 (a (sup 3) Sigma(sup +, sub g) to b (sup 3) Sigma(sup +, sub u) continuum emission. together with many strong lines assigned to the radiative decay of the gerade singlet states of H2, and to members of the H Balmer series resulting from dissociative excitation of H2.

In 1996 and 1997 the Galileo Ultraviolet Spectrometer (UVS) obtained the first measurements of Jupiter's nightside midultraviolet (MUV) polar auroral spectrum from 1620 to 3231 A at 13 A resolution. The reduced polar spectra, after removal of off-axis scattered radiation from the sunlit dayside of Jupiter, contain a spectrum that matches laboratory spectra of the H 2 continuum in the a-b dissociative emission transition. This is the first direct identification of the H 2 a-b transition in astronomy. The a-b emission is excited by electron impact exchange reactions with H 2 that peak in cross section near 15 eV. The emission threshold is at 1216 A, and the continuum peaks in intensity in the 2000-2500 A range. Jupiter's observed wavelength-integrated MUV H 2 a-b emissions (1620-3231 A) have a photon flux ∼8 times smaller than simultaneously observed wavelength-integrated far-ultraviolet (FUV) H 2 band emissions (1230-1650 A). Because the FUV H 2 emissions have an emission cross section that peaks at higher energies near 50 eV, this FUV/MUV brightness ratio is diagnostic of the secondary electron energy distribution and is consistent with a warm distribution of electrons.

A high resolution 36 mA (FWHM), optically thin emission study of the and (3, 2) Rydberg bands excited by electron impact at 100 eV has been completed in the extreme ultraviolet (EUV). A model of the perturbed rotational line intensity distribution of the bands shows the effects of electronic state mixing between the Rydberg state and the valence state. By normalizing the model to the published predissociation yield for the laboratory spectrum can be used to determine the predissociation yields for each rotational level of and 4. Based on a 25% accuracy of the model fit to the measured signal intensities it is found that the predissociation yields of the rotational levels increase as the percentage of character increases. On the other hand, the predissociation yields of the rotational levels reach a maximum for . The mean predissociation yields for and 4 levels are a function of temperature and are found to be 0.41 and 0.58, respectively at 300 K. The -dependent predissociation yields indicate that the emission cross section is a function of temperature. The remainder of the bands forming the progressions -5) from and -6) from were studied at 64 mA (FWHM) resolution. Using this composite spectrum of the two progressions the electron impact emission cross sections of the and 4 levels at 300 K were determined and compared with previous results.

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.

We have measured the extreme ultraviolet (EUV) spectrum of neon produced by electron excitation. The measurements were obtained under optically thin conditions, and at a spectral resolution of 0.5 nm full width at half maximum (FWHM). The most prominent features of the EUV spectrum between 45-80 nm are the resonance lines of Ne I at 73.6 and 74.4 nm and a multiplet of Ne II at 46.14 nm (the average value for the line center of the two closely spaced ion lines at 46.07 and 46.22 nm). Absolute emission cross sections of these lines at 300 eV were measured and compared to other previous measurements.

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.

We report medium-resolution (0.025 nm full width at half maximum (FWHM)) electron impact-induced emission spectra of CO for 20, 100, and 200 eV impact energies. The emission spectra correspond to the extreme ultraviolet transitions from the B (sup 1)Sigma(sup +)(0), and E (sup 1)Pi(0) vibronic states to the X (sup 1)Sigma(sup +)(0) ground state. The present measurements are carried out at 20 times higher spectral resolution (to separate the many blended components) compared to our previous measurements, which were at a spectral resolution of 0.5 nm FWHM. The emission cross sections corresponding to the B (sup 1)Sigma(sup +)(0) yields X (sup 1)Sigma(sup +)(0), C (sup 1)Sigma(sup +)(0) yields X (sup 1)Sigma(sup +)(0), and E (sup 1)Pi(0) yields X (sup 1)Sigma(sup +)(0) resonance transitions were measured. In addition, excitation functions (0-1 keV) extending well into the Born region have been measured for the strong transitions (B (sup 1)Sigma(sup +)(0) yields X (sup 1)Sigma(sup +)(0) and C (sup 1)Sigma(sup +)(0)) and oscillator strengths have been determined, using a modified Born approximation analytic fit to the measured excitation function.

We present the extreme ultraviolet (EUV) emission spectrum of CO_2 induced by electronimpact at 200 eV. There are 36 spectral features which are identified with a resolution of 0.5 nmover the wavelength range of 40 to 125 nm. Absolute emission cross sections were obtained for eachof these features. The EUV emission spectrum induced by electron impact consist of atomicmultiplets of CI,II and OI,II,III as well as CO and CO^+ molecular band systems produced bydissociative excitation. The CI (119.4 nm) multiplet is the strongest feature of CI with a peak crosssection of 3.61 x 10^(-19) cm^2 at 200 eV. The strongest feature of OI in the EUV spectrum is theOI (99.0 nm) multiplet with a peak cross section of 3.59 x 10^(-19) cm^2 at 200 eV.

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.

In a crossed-beam experiment under optically thin conditions the EUV spectrum of argon produced by electron impact excitation is studied. The cross sections of the resonance lines of Ar I and II are measured. The resonance lines of Ar I at 104.8 nm and 106.7 nm, and of Ar II at 91.96 nm and 93.21 nm are the most prominent features of the EUV spectrum between 40 and 110 nm. The relative-flow technique is used to measure the absolute cross sections of these lines at 200 eV. The measurements are compared with previous estimates. The measured emission cross section values at 200 eV for the Ar I lines at 104.8 nm and 106.7 nm, when compared to the electron energy loss estimates of the direct excitation cross sections, establish that cascading is larger for the Ar I resonance lines than previous emission experiments have indicated. In addition, all the emission cross sections for the Ar I and II Rydberg series in the EUV are measured at 0.5 nm resolution. The FUV spectrum is also surveyed and found to consist of Ar II multiplets from simultaneous ionization-excitation.

The electron impact induced fluorescence spectrum of N2 is measured in the 102-134 nm range at a 0.05 nm spectral resolution. The spectral measurements provide the emission cross sections of the transitions of the b 1Pi(u)-X 1Sigma(+)g Birge-Hopfield I-band system. The structure and vibrational population distribution of this system are strongly affected by a configuration interaction of the valence b 1Pi(u) and Rydberg c 1Pi(u) and o 1Pi(u) states. The excitation function (0-400 eV) for the b-X (1,2) transition is measured and a modified Born approximation analytic model is applied to calculate the oscillator strength for the b 1Pi(u)-X band system. With the exception of the v-prime = 1 level, vibrational levels of the b 1Pi(u) state predissociate with a branching ratio of between 0.95 and 1.00. Predissociation of the b 1Pi(u) state contributes approximately six percent of the total dissociation cross section of N2 by electron impact at 100 eV.

[i] Electron-impact-induced fluorescence spectra of SO 2 in the middle ultraviolet and visible wavelength regions (200-600 nm) have been measured in the laboratory using a crossed beam experiment at three electron impact energies. The emission spectra at 8, 18, and 98 eV exhibit a broad and continuous emission region extending from 225 to near 600 nm with a peak emission close to 330 nm. The quasicontinuous SO 2 bands arise primarily from direct excitation of SO 2 . At 18 and 98 eV, simultaneous excitation and dissociation of SO 2 produces distinct vibrational bands from SO and from atomic emission lines from S I, S II, O I, and O II that are superimposed on the SO 2 electronic transitions. The laboratory spectra were compared to green/violet color ratios obtained at lo by the Galileo Orbiter Solid State Imaging experiment. The laboratory spectra were also applied to the Cassini Imaging Subsystem to determine which filter combinations are particularly sensitive to electron energy, if the atmospheric gas present in the auroral atmosphere is solely or primarily SO 2 .

The intensity of UV resonance transitions excited by electron impact is determined by both direct excitation and cascade processes. The lifetime for decay by spontaneous emission from a resonant state is short (typically 10 ns). Using a pulsed electron gun technique established to separate these two effects we report a laboratory study of the UV spectrum of ${\mathrm{H}}_{2}$ attributed to cascade. We utilize the longer lifetimes (g 30 ns) for cascade channels to measure the intense spectrum of the Lyman band system $(B{}^{1}{\ensuremath{\Sigma}}_{u}^{+}--X{}^{1}{\ensuremath{\Sigma}}_{g}^{+})$ of ${\mathrm{H}}_{2}$ populated by cascade from higher lying $({\mathrm{E}\mathrm{F},\mathrm{G}\mathrm{K},\mathrm{H}}^{1}{\ensuremath{\Sigma}}_{g}^{+})$ states.

In recognition of the need for accurate collision cross-sections suitable for modeling spectroscopic observations of the planetary systems and calibrate flight instruments, NASA-JPL has determined the laboratory emission cross-sections of H, H2, N2, SO2, etc. Resonance excitation, predissociation, and non-Franck-Condon band intensity systems are determined by configuration interaction and must be taken into account in analyses of spacecraft observations. Attention is given to the application of the cross-sectional data obtained to both electron energy loss codes and models of Voyager, IUE, Galileo, and HST observations of the solar system.

We have measured the electron-impact-induced fluorescence spectrum of neon in the wavelength range 120-270 nm at a spectral resolution of 0.43 nm (FWHM). The strongest lines observed in the far-ultraviolet (FUV) spectrum of neon are assigned to terms of the doublet system of Ne 2 (2s(sup 2) 2p(sup 4)nl and the triplet system of Ne 3 (2s(sup 2)2p(sup 3)3l). Our FUV spectral data, obtained at 300 eV electron-impact energy, provide absolute emission cross sections of these Ne 2 and Ne 3 lines, and are compared to previous measurements where available. In addition, the excitation function of the strongest Ne II line observed at 191.6 nm was measured from threshold to 1000 eV electron-impact energy.

The emission spectrum of molecular hydrogen produced by electron-impact excitation at 100 eV has been measured in the wavelength range 1140-1690 A. High-resolution, optically thin spectra (delta(lambda) = 0.136 A) of the far-ultraviolet (FUV) Lyman and Werner band systems have been obtained with a newly constructed 3 m spectrometer. Synthetic spectral intensities based on the transition probabilities calculated by Abgrall et al. are in very good agreement with experimentally observed intensities. Previous modeling that utilized Allison & Daigarno band transition probabilities with Hoenl-London factors breaks down when the transition moment has significant J dependence or when ro-vibrational coupling is significant. Ro-vibrational perturbation between upsilon = 14 of the B(sup 1)Sigma(sup +, sub u) state and upsilon = 3 of the C(sup 1)Pi(sub u) state and the rotational dependence of the transition moment in the bands of the Lyman system are examined. Complete high-resolution experimental reference FUV spectra, together with the model synthetic spectra based on the Abgrall transition probabilities, are presented. An improved calibration standard is obtained, and an accurate calibration of the 3 m spectrometer has been achieved.

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at locations consistent with 6 to 30 R (sub J) auroral ovals, with much fainter emissions away form the auroral ovals. The emission spectrum is well fitted by both laboratory spectra and theoretical models of optically thin electron excited H2, with added Doppler-broadened Lyman Alpha emission. The observed Lyman Alpha emission wings extend more than 1 A from line center and appear correlated in strength with the H2 brightness. Individual rotational lines in the H2 Werner band system are resolved, allowing a determination of the H2 rotational temperature at the altitude of the emission. We derive best-fit temperatures from 400-450 to 700-750 K, with the auroral emission layer temperature changing either across the auroral oval or over several days' time. These observations demonstrate for the first time the ability to measure the observed rapid H2 temperature variations across Jupiter's auroral atmosphere.

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.

The excitation function of H Ly-alpha from the astrophysically important dissociation of electron-excited H2 over the range 10-700 eV has been measured. The analysis predicts the cross section to energies higher than the present experimental limit, and it is found that the predicted shape is in close agreement with measured results. At 6 eV the cross section is dominated by the electric dipole first Born component, while at 100 eV the electric dipole component constitutes 73 percent of the total H(2p) cross section. The cross sections of the H(2s) and H(1s) components are calculated.

Laboratory measurements of EUV emission from electron-excited N2 have been obtained at medium resolution, providing N II EUV emission cross section measurements and allowing the confirmation of recent calculations by Fawcett (1987) indicating the presence of a strong intercombination line in N II at 748.37 A. The most recently available data are used to predict the basic collisional and radiative properties of N II, the plasma diagnostic properties are briefly explored, and radiative cooling coefficients are given. Some basic properties of electron-excited N II and N2 are examined in the EUV in order to diagnose emission spectra of the earth and Titan. The N II emissions in the earth dayglow, particularly at 916 A, are much brighter than current estimates of source rates. The N II 1085 A line in the dayglow contains a significant component from dissociative photoionization excitation. The N II 1085 A, 916 A, and 670 A lines in the Titan dayglow spectrum appear to be compatible with direct electron excitation of N2.

Electron impact excitation of the b 1Pi(u) state in N2 plays a prominent role in the dissociation of the molecule and thus in the production of atomic nitrogen in planetary atmospheres. Electron impact excitation cross sections combined with electron-impact-induced fluorescence measurements can yield the corresponding dissociation cross sections. Serious discrepancies exist among excitation cross sections reported in the literature. To clarify the situation, these cross sections were measured at two impact energies using electron energy loss spectroscopy. The new results are in agreement with recent values deduced from optical measurements and fall midway between previous results which are too high or low by factors of 2.

The autoionisation energy levels of Au atoms in the vapour phase have been investigated by ejected-electron spectroscopy. Following excitation by electron impact at 15-500 eV incident-electron kinetic energy, autoionised electrons were detected with energies in the range 0-3.5 eV corresponding to 47 non-radiative transitions.

In a crossed-beam experiment the electron-impact-induced fluorescence spectrum of N2 in the extreme ultraviolet is studied at a spectral resolution of up to 0.03 nm. The optically thin experiment obtained the highest-resolution electron-impact emission spectrum of the Rydberg and valence states of N2. The spectral measurements provide the emission cross sections of each of the vibrational transitions of the Carroll-Yoshino and the Birge-Hopfield-II band systems. Laboratory vibrational-excitation cross sections arising from the mutual perturbation of the c4-prime 1Sigma(+)u and b-prime 1Sigma(+)u states by homogeneous configuration interactions are measured from 10 to 400 eV, and a modified Born approximation analytic model is given for them. The analysis leads to accurate band-system oscillator strengths. The relative emission and excitation cross sections each of the vibrational levels are compared. In addition, low-resolution measurements of the cross section of the atomic dissociation fragments (NI, NII, NIII) from 40 to 102 nm are made, and medium-resolution measurements are made of the emission cross section of the c4 1Pi(u), c5-prime 1Sigma(+)u, c5 1Pi(u), and c6-prime 1Sigma(+)u to X 1Sigma(+)g (0,0) transitions.

The ejected-electron spectrum of aluminium vapour atoms has been observed at 75 degrees with respect to an incident electron beam of 20-500 eV kinetic energy. A total of 48 lines, in the region 0-6 eV, are reported corresponding to autoionisation processes in Al I. Where possible, assignments has been made based on available experimental data and hartree-Fock-type estimates. All the prominent features in the spectrum have been accounted for. In addition, the authors have tentatively identified the 2D degrees and 2P degrees terms of the 3p3 configuration.

The alignment of the L3 shell of magnesium following electron excitation has been measured by studying the anisotropic angular distribution of electrons emitted in the Auger process 2p53s2(2P32/)-2p6(1S0)(L3-M12) (threshold 57.54 eV). Measurements of the anisotropy parameter A2 are presented for incident electron kinetic energies in the range 67.5-500 eV, and comparison is made with recent experimental and theoretical data. The results are in general agreement with the data of DuBois et al. (1981).

The ejected-electron spectrum of indium vapour between 0 and 15.5 eV has been observed at 75 degrees to an incident electron beam of 15-450 eV kinetic energy. A total of 154 lines corresponding to autoionisation processes in In I and In II are reported. Calculations have been performed and used, together with data from ultraviolet absorption measurements, to make assignments to the ejected-electron spectra.

The study of autoionization processes in metal vapour atoms has direct relevance to astrophysical and fusion data. In addition, many new laser systems are dependant on a detailed knowledge of autoionizing levels of such atoms.

Summarization: The ejected-electron spectrum of tin vapour atoms has been observed at 75 degrees to an incident electron beam of 20-1000 eV kinetic energy. A total to 71 lines are reported in the ejected-electron energy range 0-20 eV corresponding to autoionisation processes in Sn I and Sn II. Calculations have been used to make new assignments to the sp2np, d9s2p3 and d9s2p2 configurations. The results are compared with data from photoabsorption measurements, arc spectra and theoretical calculations. Παρουσιάστηκε στο: Journal of Physics B: Atomic and Molecular Physics

The polarization of Lyman-a radiation, produced by electron-impact excitation of atomic hydrogen, has been measured over the extended energy range from near threshold to 1800 eV. Measurements were obtained in a crossed-beam experiment using a silica-reflection linear polarization analyzer in tandem with a vacuum-ultraviolet monochromator to isolate the emitted line radiation. Comparison with various theoretical calculations shows that the present experimental results are in good agreement with theory over the entire range of electron-impact energies and, in particular, are in excellent agreement with theoretical convergent-close-coupling (CCC) calculations performed in the present work. Our polarization data are significantly different from the previous experimental measurements of Ott, Kauppila, and Fite.

We have developed a simple compact electron impact laboratory source of UV radiation whose relative intensity as a function of wavelength has an accuracy traceable to the fundamental physical constants (transitions probabilities and excitation cross sections) for an atomic or molecular system. Using this laboratory source, calibrated optically thin vacuum ultraviolet (VUV) spectra have been obtained and synthetic spectral models developed for important molecular band systems of H(2) and N(2) and the n(1)P(0) Itydberg series of He. The model spectrum from H(2) represents an extension of the molecular branching ratio technique to include spectral line intensities from more than one electronic upper state. The accuracy of the model fit to the VUV spectra of H(2) and N(2) is sufficient to predict the relative spectral intensity of the electron impact source and to serve as a primary calibration standard for VUV instrumentation in the 80-230-nm wavelength range. The model is applicable to VUV instrumentation with full width at half-maximum >/= 0.4 nm. The present accuracy is 10% in the far ultraviolet (120-230 nm), 10% in the extreme ultraviolet (EUV) (90-120 nm), and 20% in the EUV (80-90 nm). The n(1)P(0) Rydberg series of He has been modeled to 10% accuracy and can be considered a primary calibration standard in the EUV (52.2-58.4 nm). A calibrated optically thin spectrum of Ar has been obtained at 0.5-nm resolution and 200-eV electron impact energy to 35% accuracy without benefit of models over the EUV spectral range of 50-95 nm. The Ar spectrum expands the ultimate range of the VUV relative calibration using this source with the four gases, He, Ar, H(2), and N(2), to 50-230 nm. The calibration of the Galileo orbiter ultraviolet spectrometer for the upcoming Jupiter mission has been demonstrated and compared to results from other methods.

Emission spectrum of O2 from 115 to 300 nm induced by electron impact at 200 eV was obtained using a crossed-beam configuration under optically thin conditions. The second negative system of O2(+) was observed in the range 186-300 nm. Model calculations were performed to derive the contribution made by the second negative system of O2(+) to auroral spectra in the same wavelength range. Observations of the spectral region from 140 to 185 nm, carried out to verify the report of Erdman and Zipf (1986) on the O or O(+) transitions showed no detectable O or O(+) transitions with a cross section upper limit of 10 to the -21 sq cm.