The dissociative photoionization of methane in the VUV

Abstract

The dissociative photoionization of CH4 and CD4 has been studied using synchrotron radiation within the energy range of 12-60 eV. The mass spectra of secondary CHn+/CDn+ ions have been found to display significant isotope effects and to depend on the target gas temperature. The kinetic energy spectra of the fragment protons and deuterons have also been determined and it is shown that, in addition to direct photoionization, intermediate, superexcited states play an important role in the photodissociative ionization process.

Modeling of parasitic plasma under the divertor roof baffle

“…Photoionization collisions were implemented via a MonteCarlo collision algorithm [5]. A total photoionization cross-section r m = 4.2 · 10 À17 cm 2 [6] was used in the simulations. Correspondingly, the resulting secondary electrons had an energy E e = E m À E i = 6 eV (here E i = 12.6 eV is the methane ionization energy).…”

Formation of protons from dissociative ionization of methane induced by 54 eV electrons

“…Extensive studies of the ionization and dissociation of molecules have been carried out in previous studies by using various projectiles such as ions [1][2][3], photons [4][5][6][7], and electrons [8][9][10]. The main purposes of such studies are to investigate the various decay pathways and to clarify which parameters determine these decay pathways.…”

“…Its ground-state electronic configuration is (1a 1 ) 2 (2a 1 ) 2 (1t 2 ) 6 . The dissociation of methane can be a model system for our understanding of some basic physical and chemical processes, for example, the breakup of the C-H chemical bond.…”

“…However, it was difficult to give any decisive conclusions regarding the intermediate states where the protons were produced. Latimer et al measured the KEDs of proton fragments in their study of the dissociation of methane induced by synchrotron radiation for photon energies from 21.6 to 56.6 eV [6]. Three groups of protons were observed with kinetic energies either below 1.2 eV, around 2.2 eV, or around 3.7 eV.…”

Vacuum-UV negative photoion spectroscopy of CH4

“…There have been many studies of the dissociation products following ionisation of CH 4, revealing the fragmentation dynamics of an energy-selected CH 4 + cation [7,9,[17][18][19], and detailed Lyman-α photofragmentation studies have also been undertaken [2,20]. Total photoabsorption cross sections have been measured in the vacuum-UV range of 10-30 eV many times [21][22][23][24][25], with cross sections ranging from ca.…”