Electron impact excitation of methane: determination of appearance energies for dissociation products

Abstract

In this work, we present an experimental study of dissociative excitation of CH 4 utilizing a crossed electron molecular beam experiment. Methane was excited by nearly monochromatic electrons generated by a trochoidal electron monochromator. The dissociative products were identified on the basis of the emission spectra in the ultraviolet-visible (UV/VIS) spectral range. The excitation functions were recorded as the function of the electron energy for different emission bands of the fragments (Balmer series for H: n = 3,4 . . . 9→2, and moreover, CH: A 2 →X 2 , CH: B S 0 ). From the experimental data we have determined the threshold energies for excitation of particular fragments. Present experimental results indicate that the threshold energies for some dissociative excitation channels could be lower by ∼1-2 eV in comparison to earlier studies and indicate that different dissociative processes may be operative at the threshold than assumed in the former studies.

Dissociative electron attachment and dipolar dissociation in ethylene

“…The shape is reminiscent of typical electronic excitation functions obtained in emission spectroscopy of fragments excited by electron impact of ethylene (Aarts et al 1971). This clearly indicates that super excited states are formed as intermediates which decay by DD, fluorescence or auto ionization (Danko et al 2013). Moreover, the DD ion yield between 40 and 90 eV may indicate several peaks and shoulders.…”

Towards graphane field emitters

“…We note a rich spectrum containing various lines characteristic of a low carbon content hydrogen plasma. These include CH lines at 387.1 nm, 390.0 nm, 431.4 nm, and 494.1 nm, in addition to various sub-bands associated with CH(B 2 S À / X 2 P) emission (380-415 nm); 41 cumulatively suggesting partial etching of the GF and liberation of atomic C into the ambient. 42,43 Residual ion species, such as O + (411.2 nm) and N + (408.1 nm), are also noted.…”

Independent atom model description of multiple ionization of water, methane, and ammonia molecules by proton impact

“…These observations lead to the conclusion that the IAM-PCM approach is very strong in predicting net cross sections (dominated by the q = 1 removal cross sections), but need to be tested on a case-by case basis for the higher-q predictions. Discrete electronic excitations of the investigated molecules can also lead to fragmentation [43], and may also show different behavior among them. Further experimental work on such molecules containing multiple hydrogen bonds, especially experiments capable of proton-proton coincidences are needed to resolve some of the remaining questions of this work.…”