The High-Resolution Extreme-Ultraviolet Spectrum of N2 By Electron Impact

We have analyzed high-resolution (FWHM = 0.2 Å) extreme-ultraviolet (EUV, 800-1350 Å) laboratory emission spectra of molecular nitrogen excited by an electron impact at 20 and 100 eV under (mostly) optically thin, single-scattering experimental conditi

H_2 fluorescence spectrum from 1200 to 1700 Å by electron impact: Laboratory study and application to Jovian aurora

A combined experimental study of the fluorescence spectrum of H_2 at wavelengths of 1200-1700 Å by electron impact and its application to modeling the Jovian aurora have been carried out. Our laboratory data suggest that at 100 eV the relative cross sections for direct excitation of Lyɑ, Lyman bands (B^1Σ_u^+-X^1Σ_g^+), and Werner bands (C^1π_u-X^1Σ_g^+) are 1, 2.3±0.6, and 2.6±0.5, respectively, in conflict with Stone and Zipfs (1972) results for the Werner bands. Cascade from E,F^1Σ_g^+ states contributes an additional 31% to the B^1Σ_u^+ state population. It is shown that the most likely fate for the metastable H(2^2S) atoms produced in the Jovian aurora is collisional quenching to H(2^2P), and this could add as much as 60% to the predicted Lyɑ emission. On the basis of detailed atmospheric and radiative transfer modeling, we conclude that the recent IUE and Voyager observations are consistent with precipitation of electrons with energy in the range of 1-30 keV or other energetic particles that penetrate to number densities of 4 X 10^(10)-5 X 10^(13) cm^(-3) or column densities of 5 X 10^(17)-2 X 10^(20) cm^(-2) in the atmosphere. The globally averaged energy flux and production of hydrogen atoms are 0.5-2 ergs cm^(-2) s^(-1) and 1-4 X 10^(10) atoms cm^(-2) s^(-1), respectively

Titan airglow spectra from Cassini Ultraviolet Imaging Spectrograph (UVIS): EUV analysis

peer reviewedaudience: researcher, professional, studentWe present the first UV airglow observations of Titan's atmosphere by the Ultraviolet Imaging Spectrograph (UVIS) on Cassini. Using one spectral channel in the EUV from 561-1182 Å and one in the FUV from 1115-1913 Å, UVIS observed the disk on 13 December, 2004 at low solar activity. The EUV spectrum consists of three band systems of N[SUB]2[/SUB] (b [SUP]1[/SUP]∏[SUB]u[/SUB], b' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP], c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP] -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP]), while the FUV spectrum consists of one (a [SUP]1[/SUP]∏[SUB]g[/SUB] -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP]). Both the EUV and FUV spectra contain many N I and N II multiplets that are produced primarily by photodissociative ionization. Spectral intensities of the N[SUB]2[/SUB] c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP](v' = 0) -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP](v'' = 0-2) progression from 950-1010 Å are resolved for the first time. The UVIS observations reveal that the c[SUB]4[/SUB]' [SUP]1[/SUP]∑[SUB]u[/SUB] [SUP]+[/SUP](0) -> X [SUP]1[/SUP]∑[SUB]g[/SUB] [SUP]+[/SUP] (0) vibrational band near 958 Å is weak and undetectable, and that N I multiplets near 953.2 and 964.5 Å are present instead. Magnetospheric particle excitation may be weak or sporadic, since the nightside EUV spectrum on this orbit shows no observable nitrogen emission features and only H Ly-β

High-Resolution Electron-Impact Emission Spectrum of H 2 . I. Cross Sections and Emission Yields 900-1200 Å

High-resolution (Δλ = 115 mA) emission spectra of molecular hydrogen produced by electron-impact excitation at 100 eV have been obtained in the wavelength range 900-1200 A. The emission spectra can be assigned to transitions between the X 1Σ ground state and the 1sσgnpσu 1Σu and 1sσgnpπu 1Πu Rydberg states. Synthetic rotational line spectra based on the excitation function of Liu et al. and calculated 2pσ B 1Σ-X 1Σ, 2pπ C 1Πu-X 1Σ, 3pσ B' 1Σ-X 1Σ, and 3pπD 1Πu-X 1Σ transition probabilities of Abgrall et al. are generally found to be in good agreement with the experimental spectra in the regions where emissions from 1sσgnpσu (n ≥ 4) and 1sσgnpπu (n ≥ 4) states are negligible. Emission cross sections for D 1Π, D' 1Πu, and D'' 1Π, B' 1Σ, and B'' 1Σ states are obtained by measuring the emission intensities from these states relative to those from the B 1Σ,C 1Πu, and D 1Π states. A high- resolution EUV calibration technique is established. At 100 eV the emission cross sections of the D 1Πu, D' 1Πu, D'' 1Πu, B' 1Σ, and B'' 1Σ states are measured to be (2.8 ± 0.4) × 10-18, (6.3 ± 1.3) × 10-19, (5.9 ± 1.7) × 10-20, (2.1 ± 0.3) × 10-18, and (1.6 ± 0.4) × 10-19 cm2, respectively. In addition, the vibrational emission cross sections have been compared to the estimated excitation cross sections to obtain the predissociation yields for selected vibrational levels of the D 1Π, D' 1Π and D'' 1Π states. The B' 1Σ state is inferred to have very significant excitation into the H(1s)+H(2p,2s) dissociative continuum

Medium-resolution studies of extreme-ultraviolet emission from CO by electron impact

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

Jupiter: aerosol chemistry in the polar atmosphere

Aromatic compounds have been considered a likely candidate for enhanced aerosol formation in the polar region of Jupiter. We develop a new chemical model for aromatic compounds in the Jovian auroral thermosphere/ionosphere. The model is based on a previous model for hydrocarbon chemistry in the Jovian atmosphere and is constrained by observations from Voyager, Galileo, and the Infrared Space Observatory. Precipitation of energetic electrons provides the major energy source for the production of benzene and other heavier aromatic hydrocarbons. The maximum mixing ratio of benzene in the polar model is 2 × 10^(-9), a value that can be compared with the observed value (2^(+2)_(-1)) × 10^(-9) in the north polar auroral region. Sufficient quantities of the higher ring species are produced so that their saturated vapor pressures are exceeded. Condensation of these molecules is expected to lead to aerosol formation

All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe

The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in the 200 keV to 10 GeV energy range with a wide field of view, good spectral resolution, and polarization sensitivity. Therefore, AMEGO is key in the study of multimessenger astrophysical objects that have unique signatures in the gamma-ray regime, such as neutron star mergers, supernovae, and flaring active galactic nuclei. The order-of-magnitude improvement compared to previous MeV missions also enables discoveries of a wide range of phenomena whose energy output peaks in the relatively unexplored medium-energy gamma-ray band

Cassini UVIS observations of Titan nightglow spectra

In this paper we present the first nightside EUV and FUV airglow limb spectra of Titan showing molecular emissions. The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed photon emissions of Titan's day and night limb-airglow and disk-airglow on multiple occasions, including during an eclipse observation. The 71 airglow observations analyzed in this paper show EUV (600-1150 Å) and FUV (1150-1900 Å) atomic multiplet lines and band emissions arising from either photoelectron induced fluorescence and solar photo-fragmentation of molecular nitrogen (N[SUB]2[/SUB]) or excitation by magnetosphere plasma. The altitude of the peak UV emissions on the limb during daylight occurred inside the thermosphere at the altitude of the topside ionosphere (near 1000 km altitude). However, at night on the limb, a subset of emission features, much weaker in intensity, arise in the atmosphere with two different geometries. First, there is a twilight photoelectron-excited glow that persists with solar depression angle up to 25-30 degrees past the terminator, until the solar XUV shadow height passes the altitude of the topside ionosphere (1000-1200 km). The UV twilight glow spectrum is similar to the dayglow but weaker in intensity. Second, beyond 120° solar zenith angle, when the upper atmosphere of Titan is in total XUV darkness, there is indication of weak and sporadic nightside UV airglow emissions excited by magnetosphere plasma collisions with ambient thermosphere gas, with similar N[SUB]2[/SUB] excited features as above in the daylight or twilight glow over an extended altitude range

The Middle Ultraviolet-Visible Spectrum of H2 Excited by Electron Impact

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