Kenichi Okutsu

An ion imaging apparatus with a double linear reflectron mass spectrometer has been developed, in order to measure velocity and angular distributions of mass-analyzed fragment ions produced by photodissociation of mass-selected gas phase complex ions. The 1st and the 2nd linear reflectrons were placed facing each other and controlled by high-voltage pulses in order to perform the mass-separation of precursor ions in the 1st reflectron and to observe the focused image of the photofragment ions in the 2nd reflectron. For this purpose, metal meshes were attached on all electrodes in the 1st reflectron, whereas the mesh was attached only on the last electrode in the 2nd reflectron. The performance of this apparatus was evaluated using imaging measurement of Ca+ photofragment ions from photodissociation reaction of Ca+ Ar complex ions at 355 nm photoexcitation. The focused ion images were obtained experimentally with the double linear reflectron at the voltages of the reflection electrodes close to the predictions by ion trajectory simulations. The velocity and angular distributions of the produced Ca+ ([Ar] 4p(1), 2P(3/2)) ion were analyzed from the observed images. The binding energy D-0 of Ca+ Ar in the ground state deduced in the present measurement was consistent with those determined theoretically and by spectroscopic measurements. The anisotropy parameter beta of the transition was evaluated for the first time by this instrument. Published by AIP Publishing.

We have observed fragment ion images produced by ultraviolet photodissociation of Mg+BrCH3 complex ions using a reflectron time-of-flight mass spectrometer combined with an imaging detector. The BrCH3+ fragment ion was produced after the 266-nm excitation of Mg+BrCH3. In the image of the BrCHN3+ ions, a split distribution was observed parallel to the polarization direction of the photolysis laser. In calculated potential energy curves, we found a repulsive potential correlated with a dissociation limit of Mg+BrCH3+: The calculation results indicate that the dissociation and the charge transfer occurred via non-adiabatic process after the 5(2)A' <- 1(2)A' photoexcitation. The obtained energy and angular distributions of BrCH3+ photofragments were consistent with the fast BrCH3+ formation process on the repulsive potential energy curve. Published by AIP Publishing.