Production of excited H atoms at the C 1sedge of the methane molecule studied by VUV-photon–photoion and metastable-fragment–photoion coincidence experiments

Abstract

Coincidences between neutral particles and photoions have been measured at the C 1s edge of the CH 4 molecule. These neutral particles are either vacuum ultraviolet (VUV) photons or metastable fragments and their contributions can be separated temporally. Observed VUV-photon-photoion coincidences were mostly triggered by Lyman emission in excited H atoms. Two metastable fragment-photoion channels were observed and assigned to H * -H + and H * -CH n + (n = 0-3) coincidences, where H * signifies a metastable H atom. The coincidence yields as a function of photon energy revealed all the core excitations, but were particularly enhanced just above the C 1s ionization threshold and also displayed the vibrational structure related to the core-ionized C 1s −1 state. The metastable H atoms observed in the present study were produced in highly excited Rydberg states and could be partly field ionized. The approximate kinetic energy distributions of the metastable H * atoms have been derived from the H * -H + coincidence measurements performed at the C 1s → 3p and 3d resonances as well as just above the C 1s threshold.

Yields and Time-of-Flight Spectra of Neutral High-Rydberg Fragments at the K Edges of the CO2 Molecule

“…It is well established that when the photon energy just exceeds the core IP of a molecule, a molecular parent ion can recapture a slow photoelectron in a HR orbital. ,,, Thus, if a molecule has an electron configuration val –2 after Auger decay, it becomes val –2 HR 1 after the photoelectron recapture. The two holes in the valence orbitals easily render these states dissociative.…”

“…Neutral metastable fragments have earlier been observed at the core edges of some other small molecules. − Their production is typically enhanced at all core excitations below a given core IP and more pronouncedly just above the core IP. The production above the core IP was first explained by Hikosaka et al in the case of the N 2 molecule .…”

Vacuum ultraviolet photoionization and ionic fragmentation of the isoxazole molecules

“…The measurements were carried out at the Circular Polarization (CiPo) beamline [29] We used the experimental apparatus described by Kivimäki et al [28]. It consists of a modified Wiley-McLaren time-of-flight (TOF) spectrometer, which was originally used to detect photoelectron-photoion coincidences and subsequently also neutral-particle-photoion coincidences [30]. The setup in the modified configuration can also be used to measure PEPICO spectra.…”

Soft X-ray Induced Production of Neutral Fragments in High-Rydberg States at the O 1s Ionization Threshold of the Water Molecule

“…The detector of this particular ion TOF spectrometer has previously detected Lyman radiation due to excited H atoms. 24 Such emission usually takes place in the nanosecond timescale. Characteristics of Lyman emission change in the electric field.…”

“…MCP detectors can also detect photons of sufficiently short wavelengths. The detector of this particular ion TOF spectrometer has previously detected Lyman radiation due to excited H atoms . Such emission usually takes place in the nanosecond timescale.…”