We have observed fragment ion images produced by ultraviolet photodissociation of MgBrCH complex ions using a reflectron time-of-flight mass spectrometer combined with an imaging detector. The BrCH fragment ion was produced after the 266-nm excitation of MgBrCH. In the image of the BrCH 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 + BrCH: The calculation results indicate that the dissociation and the charge transfer occurred via non-adiabatic process after the 5A' ← 1A' photoexcitation. The obtained energy and angular distributions of BrCH photofragments were consistent with the fast BrCH formation process on the repulsive potential energy curve.

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 CaAr 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, P) ion were analyzed from the observed images. The binding energy D of CaAr in the ground state deduced in the present measurement was consistent with those determined theoretically and by spectroscopic measurements. The anisotropy parameter β of the transition was evaluated for the first time by this instrument.

We have observed images of MgI fragment ions produced in ultraviolet laser photodissociation of mass-selected MgICH ions at 266 nm. Split distribution almost perpendicular to the polarization direction of the photolysis laser was observed in the photofragment image. Potential energy curves of MgICH were obtained by theoretical calculations. Among these curves, the excited complex ion dissociated along almost repulsive potentials with several avoided crossings, which was connected to MgI + CH. In the ground state of MgICH, the CHI was bonded with Mg from the iodine side, and the Mg-I-C bond angle was calculated to be 101.1°. The theoretical results also indicated that the dissociation occurred after the 5A' ← 1A' photoexcitation, where the transition dipole moment was almost parallel to the Mg-I bond axis. The MgI and CH fragments dissociated each other parallel to the direction connecting those center-of-masses, which was 67° with respect to the transition dipole moment of 5A' ← 1A' photoexcitation. Therefore, the fragment recoil direction was assumed to approach perpendicular tendency against the polarization direction under the fast dissociation process. However, calculated potential energy curves showed a complicated reaction pathway for MgI production, including nonadiabatic processes, although the experimental results indicated the fast dissociation reaction.