Cationic and Anionic Fragmentation of Dichloromethane following Inner-Shell (Cl 1s) Photoexcitation

Abstract

The cationic and anionic fragmentation of dichloromethane (CH2Cl2) molecule have been investigated in the energy range of the Cl K shell by using synchrotron radiation, ion yield spectroscopy, and electron-ion coincidence spectroscopy. Total and partial ion-yield and mass spectra have been recorded as a function of the photon energy. We were able to identify several singly and multiply charged cationic fragments and the following anionic species: H-; C-; Cl-. The present results provide the first experimental report of negative ion formation from a molecule excited at the Cl 1s edge. In addition, our electron-ion coincidence data provide strong evidence of the preservation of molecular alignment for the photodissociation of CH2Cl2 after deep core-electron resonant excitation.

Dissociative photoionization of adenine following valence excitation

“…The secondary electrons produced in the ionization region are focused by an electrostatic lens to the center of the microchannel plate detector. Negative ions may also be produced in the photoionization process, for instance, via formation of ion pairs or via multi‐step mechanisms, as previously reported,14 but the corresponding cross‐section in the energy range of the present work is negligible. The gas needle was kept at ground potential and the emergent photon beam flux was recorded by a light sensitive diode.…”

State-selective enhanced production of positive ions and excited neutral fragments of gaseous CH2Cl2following ClLu1, Chen2, Lee3 et al. 2010Phys. Rev. A

“…This enhancement is proposed to reflect an ultrafast dissociation channel, i.e., fragmentation before core decay [33,34,36]. Based on electron-ion-ion coincidence measurements, the Cl 1s → 10 a 1 * resonance of gaseous CH 2 Cl 2 exhibits an ultrafast dissociation of the C-Cl bond [24]. The enhanced CH 2 + yield via the Cl 2p → 10 a * 1 excitation of gaseous CH 2 Cl 2 , shown in Fig.…”

“…These two peaks have hence dominantly localized valence-orbital character [23]. Based on quantum-chemical calculations (MP4/6-311G * * full level of theory), the absorption peaks (labeled 1 and 1 ) are assigned to transitions from the Cl (2P 3/2 , 1/2 ) initial states to the 10 a * 1 orbitals [24]. The next doublet structures (labeled 2 and 2 ) are attributed to excitations to the 4 b * 1 orbital, but the decreased intensity of lines labeled 2 and 2 in the solid TEY spectrum indicates that these two lines have also some Rydberg character, particularly for the absorption labeled 2 .…”

Role of ultrafast dissociation in the fragmentation of chlorinated methanes

“…The fragmentation has been widely studied using electron-ion coincidence techniques [10][11][12][13][14][15][16][17] . The electronic structure of the valence region and its relationship to fragmentation has been investigated by various UV and VUV excitation studies [18][19][20][21][22][23] .…”