Combined Experimental and Theoretical Studies on Electron Transfer in Potassium Collisions with CCl₄

Abstract

Negative ion formation in electron transfer experiments from fast neutral potassium (K) atom collisions with neutral tetrachloromethane (CCl 4 ) molecules has been investigated in the laboratory frame range of 8−1000 eV. Comprehensive calculations on the electronic structure were performed for CCl 4 in the presence of a potassium atom and used to help analyze the lowest unoccupied molecular orbitals participating in the collision process. Additionally, K + energy loss produced in the forward direction has served to further our knowledge on the electronic state spectroscopy of CCl 4 . A vertical electron affinity of −0.79 ± 0.20 eV has been obtained and assigned to a purely repulsive transition from CCl 4 ground state to the 2 T 2 state of the temporary negative ion yielding Cl − formation. Other features in the energy loss spectrum were observed for the first time and related to Cl 2 − , CCl 2 − , and CCl 3 − formation. Special attention is also given to the unresolved feature corresponding to a positive electron affinity of 0.24 ± 0.2 eV, assigned to a vibrationally hot transition from CCl 4 ground state into the triply degenerate 2 T 2 excited state of the negative ion. The combined time-of-flight mass spectrometry together with K + energy loss data represents the most comprehensive assignment of the tetrachloromethane anion yields and the role of CCl 4 electronic states in collision induced dissociation to date.

Sensing the ortho Positions in C6Cl6 and C6H4Cl2 from Cl2− Formation upon Molecular Reduction

“…Thus, the experimental thresholds of formation assumed that K* in a 4p state would result in values at lower energies than those reported in these experiments. Such behavior has been previously reported in other energy loss data from potassium collisions with pyrimidine [ 36 ], halothane [ 37 ], tetrachloromethane [ 28 ] and methanol [ 38 ]. The K o hyp beam intensity was monitored at the entrance of the collision chamber by a surface ionization detector of the Langmuir-Taylor type.…”

“…The TNI can have a long lifetime relative to a competing autodetachment process, allowing it to be detected within the experimental μs time window regime. In such a redox reaction, the energy deposited in the TNI may be redistributed through the different internal degrees of freedom, while direct and statistical dissociation may lead to bond excision, usually with the excess electron at a highly electronegative site of the molecule, e.g., halogen atoms [ 28 ] or the nitro group in radiosensitizers [ 24 , 29 , 30 ].…”

“…The beam energy resolution for TOF mass spectra collection in the collision energy range investigated was ~0.6 eV. Mass calibration was performed using the well-known fragmentation patterns from collisions of potassium atoms with nitromethane [ 39 ] and/or carbon tetrachloride molecules [ 28 ]. Background measurements were obtained and subtracted from the sample measurements.…”

Bound Electron Enhanced Radiosensitisation of Nimorazole upon Charge Transfer

“…The typical base pressure in the collision chamber was 6 × 10 −5 Pa and the working pressure was 2 × 10 −4 Pa. Mass spectra (resolution m/∆m ≈ 800) were obtained by subtracting background measurements (without the sample) from the sample measurements. Mass calibration was performed on the basis of the well-known anionic species formed after potassium collisions with nitromethane [37] and tetrachloromethane [46].…”

Methanol Negative Ion Fragmentation Probed in Electron Transfer Experiments

“…Such behavior has been previously reported in other energy loss data from potassium collisions with pyrimidine, 22 halothane, 24 and tetrachloromethane. 25 K hyp o beam intensity is monitored at the entrance of the collision chamber by a surface ionization detector of the Langmuir− Taylor type. Subsequently, the K hyp o beam crosses at right angles with an effusive target beam, which is admitted to vacuum through a 1 mm diameter capillary from an external sample holder.…”