Electron-impact Emission Cross Sections Research Articles

High resolution EUV emission spectroscopy of the and 4 levels by electron impact

A high resolution 36 mÅ (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 mÅ (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.

Electron-impact emission cross sections of Ar

Electron impact emission cross sections of Ar were measured for the , and transitions from the threshold to 1000 eV by a polarization-free method. Two different methods were used in determining absolute emission cross sections for the first resonance lines. The first method is to measure the cascade cross sections to the 4s state by detecting visible to near-infrared radiation and the total cascade cross section was then combined with the level excitation cross section to the 4s state to give the emission cross section for the resonance line. The second method is to measure the vacuum ultraviolet sensitivity of the apparatus and an absolute emission cross section for the resonance line was obtained by comparing its spectral intensity with that of the Lyman- radiation produced from by electron impact. The two results showed good agreement within the experimental errors. The level excitation cross sections to the and states were obtained by subtracting the total cascade cross section to these levels from the corresponding emission cross sections.

Electron impact excitation cross section studies of methane and acetylene

We have measured the electron impact emission cross sections for CH4 and C2H2 at 200 eV in a crossed beam laboratory system. Included in the study are all vacuum ultraviolet (VUV) emission features from 40 to 200 nm. The features are entirely from the atomic dissociation fragments (C i, C ii, and H). The Lyman series of H is observed to truncate near principal quantum number n=10 due to the long lifetime and to the high kinetic energy of the excited H fragments. The threshold region of the excitation functions has been measured at an energy resolution of 0.2–1.0 eV for the Lyman-α and Lyman-β transitions of H and C i (165.7, 193.1 nm) multiplets; and several distinct appearance potentials (AP) have been detected. For example, appearance potentials of Lyman-α from dissociation of CH4 and C2H2 are noted at several energies, including the first observations of a Lyman-α AP from C2H2 at 16.3 eV.

A study of the extreme ultraviolet spectrum of O2 by electron impact

We have measured in the laboratory the electron impact emission cross sections for O2 at 200 eV. Included in the study are all emission features in the extreme ultraviolet from 40 to 131 nm at a resolution of 0.5 nm. The features are entirely from the dissociation products (OI, OII, OIII). Additionally we have measured the excitation functions from 0 to 400 eV for characteristic OI multiplets at 98.9 and 102.6 nm and for OII multiplets at 53.9 and 83.3 nm. We find the OI multiplets are formed near the dissociation limit whereas the OII multiplets have a threshold about 10 eV above the dissociation limit. We also determine the total VUV emission cross section of O2 from 40 to 200 nm and indicate the effects of autoionization to the measured emission spectrum.

VUV-standard for beam experiments

A line source is proposed as an intensity standard for the VUV, based on experimental electron impact emission cross sections of gases. The source is calibrated against synchrotron radiation and it is intended for an in situ calibration in electron and ion beam excitation and ionization studies.