High-resolution (e, 2e + ion) study of electron-impact ionization and fragmentation of methane

Abstract

The ionization and fragmentation of methane induced by low-energy (E0 = 66 eV) electron-impact is investigated using a reaction microscope. The momentum vectors of all three charged final state particles, two outgoing electrons, and one fragment ion, are detected in coincidence. Compared to the earlier study [Xu et al., J. Chem. Phys. 138, 134307 (2013)], considerable improvements to the instrumental mass and energy resolutions have been achieved. The fragment products CH4 (+), CH3 (+), CH2 (+), CH(+), and C(+) are clearly resolved. The binding energy resolution of ΔE = 2.0 eV is a factor of three better than in the earlier measurements. The fragmentation channels are investigated by measuring the ion kinetic energy distributions and the binding energy spectra. While being mostly in consistence with existing photoionization studies the results show differences including missing fragmentation channels and previously unseen channels.

Breakdown curves of CH2(+), CH3(+), and CH4(+) molecules

“…The width of the second component ((1t 2 ) −1 ) has been increased and another component added. It mimics the experimental extension reported by Ren et al (2015) or van der Wiel et al (1976). For CH 3 , the BEB second contribution ((1e ) −1 )), was moved to lower energies by 0.25 eV.…”

“…The values have been normalized to the most intense species (intact species here), as is done in 8. For CH 4 , the first component ((1t 2 ) −1 ) of BEB IED has been replaced by the experimental (e,2e) value from Ren et al (2015). The difference is small, but has some effect because it lies in the abrupt opening of the first dissociation channel (see Fig.…”

“…Many studies have been performed in this context of astrochemistry on CH (+) y (e.g., van Dishoeck et al 1980van Dishoeck et al , 1996van Dishoeck et al , 2006Bettens & Collins 1998;Blint et al 1976;Federer et al 1984;Heays et al 2017;Kim et al 1975;Larson et al 1998;Plasil et al 2011;Puglisi et al 2018;Rimmer & Helling 2016;Talbi & Saxon 1992;Thomas et al 2013;Vejby-Christensen et al 1997;Zanchet et al 2016). It is also of interest in planetary atmospheric sciences where CH (+) y is often an important ingredient (e.g., Gans et al 2013;Liu & Shemansky 2006;Pei & Farrar 2013;Salehzadeh & Kirchner 2017;Sheehan & St.-Maurice 2004;Tarnovsky et al 1996;Au et al 1993;Lecointre et al 2008), in plasma sciences (e.g., Lecointre et al 2008Lecointre et al , 2009Deutsch et al 2000;Irikura 2017;Janev & Reiter 2002;Reiter & Janev 2010), in molecular physics (e.g., Frey & Davidson 1988;Kari & Csizmadia 1967;Jensen et al 2002;Ren et al 2015;Samson et al 1989;Lodriguito et al 2009;Theodorakopoulos & Petsalakis 1991;…”

An (e, 2e+ ion) study of electron-impact ionization and fragmentation of tetrafluoromethane at low energies

“…The BE is the vertical transition energy required to ionize a particular electronic orbital [56][57][58].…”

Experimental and theoretical triple-differential cross sections for tetrahydrofuran ionized by low-energy 26-eV-electron impact

“…In order to cover a large solid angle for the detection of the fragment ions, a pulsed electric field has been applied for ion extraction. In this way, significantly improved mass and energy resolutions have been achieved [20], [21].…”