Velocity map imaging apparatus applicable to a study of multiple photofragmentation of C60

ISRN Physical Chemistry

Kaflé

et al. 2012

Self Cite

A photoionization spectrometer for velocity map imaging has been developed for measuring the scattering distribution of fragment ions from polyatomic molecules. The spectrometer contains a mass gate and an ion reflector which are able to discriminate ions with a particular mass-to-charge ratio m/z. The basic functions and feasibility of these devices were tested experimentally and theoretically. First, the photoions from Kr and C 60 were extracted into a time-of-flight (TOF) mass spectrometer by a transient or continuous electrostatic field. When the pulse application on the mass gate was tuned to the arrival timing of ions with a specific m/z, the peak of the selected ions alone was present on a TOF spectrum. Second, compatibility between velocity map imaging and ion discrimination was investigated by the computer simulations of the ion trajectories of photofragments from C 60 . A pulsed voltage was applied to the mass gate synchronously with the arrival timing of C 58 + ions. The initial three-dimensional velocity distribution of C 58 + was projected onto the image plane with an energy resolution better than 10 meV. The C 58 +

Section: Introductionmentioning

confidence: 99%

Design of Velocity Map Imaging Spectrometer Equipped with a Mass Gate Discriminating Particular Photofragments

ISRN Physical Chemistry

Kaflé

et al. 2012

Self Cite

Communication: Mass-analyzed velocity map imaging of thermal photofragments from C60

The Journal of Chemical Physics

2010

The velocity distributions of the fragments produced by dissociative photoionization of C(60) have been measured in the extreme UV region for the first time, by using a flight-time resolved velocity map imaging technique combined with a high-temperature molecular beam and synchrotron radiation. Values of the average kinetic energy release were estimated at six different photon energies with respect to five reaction steps of sequential C(2) ejection, starting from C(60)(2+)-->C(58)(2+)+C(2) to C(52)(2+)-->C(50)(2+)+C(2). The translational temperatures of the fragment ions were found to be lower than those obtained by laser multiphoton absorption of C(60). The kinetic energies released in the first to fourth steps increase with increasing hnu and reach 0.35-0.5 eV at hnu=102 eV, reflecting statistical redistribution of the excess energy in the transition state, whereas that in the fifth step leading to C(50)(2+) was exceptionally small.

Mass-analyzed velocity map imaging of doubly charged photofragments from C70

The Journal of Chemical Physics

2011

The velocity distributions of the fragments produced by dissociative photoionization of C(70) have been measured at several photon energies in the extreme UV region, by using a flight-time resolved velocity map imaging (VMI) technique combined with a high-temperature molecular beam and synchrotron radiation. Average kinetic energy release was estimated for the six reaction steps of consecutive C(2) emission, starting from C(70)(2+) → C(68)(2+) + C(2) to C(60)(2+)→ C(58)(2+) + C(2). The total kinetic energy generated in each step shows a general tendency to increase with increasing hν, except for the first and fifth steps. This propensity reflects statistical redistributions of the excess energy in the transition states for the above fragmentation mechanism. Analysis based on the finite-heat-bath theory predicts the detectable minimum cluster sizes at the end of the C(2)-emission decay chain. They accord well with the minimum sizes of the observed ions, if the excess energy in the primary C(70)(2+) is assumed to be smaller by ~15 eV than the maximum available energy. The present VMI experiments reveal remarkably small kinetic energy release in the fifth step, in contradiction to theoretical predictions, which suggests involvement of other fragmentation mechanisms in the formation of C(60)(2+).