Kinetic Energy Fragment Research Articles

Multiphoton Rydberg and valence dynamics of CH3Br probed by mass spectrometry and slice imaging.

The multiphoton dynamics of CH3Br were probed by Mass Resolved MultiPhoton Ionization (MR-MPI), Slice Imaging and Photoelectron Imaging in the two-photon excitation region of 66 000 to 80 000 cm-1. Slice images of the CH3+ and Br+ photoproducts of ten two-photon resonant transitions to np and nd Rydberg states of the parent molecule were recorded. CH3+ ions dominate the mass spectra. Kinetic energy release spectra (KERs) were derived from slice and photoelectron images and anisotropy parameters were extracted from the angular distributions of the ions to identify the processes and the dynamics involved. At all wavelengths we observe three-photon excitations, via the two-photon resonant transitions to molecular Rydberg states, forming metastable, superexcited (CH3Br#) states which dissociate to form CH3 Rydberg states (CH3**) along with Br/Br*. A correlation between the parent Rydberg states excited and CH3** formed is evident. For the three highest excitation energies used, the CH3Br# metastable states also generate high kinetic energy fragments of CH3(X) and Br/Br*. In addition for two out of these three wavelengths we also measure one-photon photolysis of CH3Br in the A band forming CH3(X) in various vibrational modes and bromine atoms in the ground (Br) and spin-orbit excited (Br*) states.

Multielectron dissociative ionization of CH 3I clusters under moderate intensity ps laser irradiation

The interaction of 35 ps laser pulses with methyl iodide clusters in the intensity region of 10 12–3 × 10 13 W/cm 2 is studied at λ = 266, 532 and 1064 nm by means of time-of-flight mass spectrometry. At λ = 532 and 1064 nm the multielectron dissociative ionization (MEDI) of clusters results in highly charged atomic fragment (up to I 7+) ion production of high kinetic energy. The explosion of the multiple charged cluster ions is found to be isotropic, while an asymmetric charge distribution prior to their fragmentation is observed. Moreover, negative ion formation is observed. The MEDI of clusters exhibits a dependence on laser polarization and the intensity thresholds for the observation of the fragment ions are determined for linear and circular laser polarization. These intensity thresholds are found to be about three orders of magnitude lower than those reported by experiments with 35 ps laser pulses on CH 3I monomers. For the observed MEDI of (CH 3I) n clusters a mechanism is proposed. According to this mechanism, the clusters are initially single ionized by multiphoton absorption and an internal electric field is created within the cluster, which distorts the potential barriers. This distortion increases the probability for electron tunneling even at relatively low laser intensities, giving thus rise to the formation of negatively charged moieties within the clusters, which prevent the cluster elongation and facile further the tunneling process. This procedure results in a higher distortion of the internal barriers and an increased ionization of the clusters, which, due to increased repulsive forces, finally fragment leading to multiple charged high kinetic energy fragment ion production.

Cross sections for the dissociative electron attachment to ozone

The cross sections for the dissociative electron attachment (DEA) to ozone have been measured. Care has been taken to collect all the high kinetic energy fragments such that the present absolute DEA cross section measurements are believed to be the most accurate measurements made across the range from 0 to 10 eV for ozone. Our results have been interpreted with the help of both existing data in the literature and quantum chemical calculations performed on the neutral and negative-ion states of ozone.

Fragmentation of (η5‐cyclopentadienyl)dicarbonyl‐acyliron complexes under electron impact

AbstractFragmentation patterns under electron impact of selected (η5‐cyclopentadienyl)dicarbonylacyliron complexes were studied. Fragmentation pathways were confirmed using accurate mass measurements and B/E = constant and mass‐analysed ion kinetic energy fragment ion spectra.

Molecular dissociation by electron impact: High Rydberg fragments from methane, ethylene, and ethane

Electron impact dissociation of CH4, C2H4, and C2H6 produces high Rydberg H and C fragments. Time-of-flight measurements and excitation functions help to characterize the molecular processes involved. Although details differ, the three molecules display similar dissociation behavior; relatively low kinetic energy fragments (≲8 eV) arise from states between 19 and 30 eV, higher kinetic energy fragments from states between 30 and 40 eV (states most likely with doubly ionized cores), and even higher kinetic energy fragments (up to 18 eV) from states above 40 eV. Comparisons of high Rydberg kinetic energy spectra with available ion kinetic energy spectra show general agreement confirming the utility of the core ion model for polyatomic molecules.

Kinetic Energy Release and Metastable Transitions II. The Decomposition of Doubly-Charged Ions of Aliphatic and Alicyclic Hydrocarbons

Abstract The decompositions of doubly-charged ions given by a number of C3 -C8 aliphatic and alicyclic hydrocarbons have been investigated in a double-focusing mass spectrometer. Many processes were found in which high kinetic energy CH3 + and C2H3 + ions are formed. Doubly-charged ions fragment by more than one route and in many cases, high kinetic energy fragment ions are formed in at least two different ways. Metastable transitions common to several compounds were observed, the intensities rising as the degree of unsaturation increased.

Auftrittspotentialmessungen an ionisierten Molekülbruchstücken mit kinetischer Anfangsenergie

A 60°-magnetic mass spectrometer of high sensitivity (smallest detectable signal ca. 10-19 amps) has been used for the measurement of appearance potentials of high kinetic energy fragment ions from propane. The appearance potential values show that these ions originate both from singly and doubly charged molecular ions. The ions C2H5 +, C2H3 +, C2H2 +, CH3 +, CH+, H2 +, and H+ are produced by at least two reactions. However, only one process was found for the ions C2H4 + and C2H+. The calculated and measured appearance potentials agree within some tenths of a volt. The kinetic energy was measured by the deflection method. The accuracy in the determination of appearance potentials is largely determined by the high resolution in kinetic energy measurement.