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  1. We have analyzed medium-resolution (FWHM = 1.2 nm) Middle UltraViolet (MUV; 180–280 nm) laboratory emission spectra of CO excited by electron impact at 15, 20, 40, 50, and 100 eV under single-scattering conditions at 300 K. The MUV emission spectra at 100 eV contain the Cameron Bands (CB) CO(a 3Π → X 1Σ+), the Fourth Positive Group (4PG) CO(A 1Π → X 1Σ+), and the First Negative Group (1NG) CO+(B 2Σ+ → X 2Σ) from direct excitation and cascading-induced emission of an optically-thin CO gas. We have determined vibrational intensities and emission cross sections for these systems, which are important for modeling UV observations of the atmospheres of Mars and Venus. We have also measured the CB ‘glow’ profile about the electron beam of the long-lived CO (a 3Π) state and determined its average metastable lifetime of approximately 3 ± 1 ms. Optically-allowed cascading from a host of triplet states has been found to be the dominant excitation process contributing to the CB emission cross section at 15 eV, most strongly by the d 3Δ and a' 3Σ+ electronic states. We normalized the CB emission cross section at 15 eV electron impact energy by Multi-Linear Regression (MLR) analysis to themore »blended 15 eV MUV spectrum over the spectral range of 180–280 nm, based on the 4PG emission cross section at 15 eV that we have previously measured (Ajello et al., 2019). We find the Cameron band total emission cross section at 15 eV to be (7.65 ± 2.68) × 10−17 cm2.« less
  2. We have measured in the laboratory the far ultraviolet (FUV: 125.0–170.0 nm) cascade-induced spectrum of the Lyman-Birge-Hopfield (LBH) band system (a 1Πg → X 1Σg+) of N2 excited by 30–200 eV electrons. The cascading transition begins with two processes: radiative and collision-induced electronic transitions (CIETs) involving two states (a′ 1Σu− and w 1Δu → a 1Πg), which are followed by a cascade induced transition a 1Πg → X 1Σg+. Direct excitation to the a-state produces a confined LBH spectral glow pattern around an electron beam. We have spatially resolved the electron induced glow pattern from an electron beam colliding with N2 at radial distances of 0–400 mm at three gas pressures. This imaging measurement is the first to isolate spectral measurements in the laboratory of single-scattering electron-impact-induced-fluorescence from two LBH emission processes: direct excitation, which is strongest in emission near the electron beam axis; and cascading-induced, which is dominant far from the electron beam axis. The vibrational populations for vibrational levels from v′=0–2 of the a 1Πg state are enhanced by CIETs, and the emission cross sections of the LBH band system for direct and cascading-induced excitation are provided at 40, 100, and 200 eV