Control of photodissociation reaction of fluoromethane molecules using deformation in core-excited state

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At first, a Wiley-McLarlen type time-of-flight (TOF) mass spectrometer equipped with a two-dimensional position-sensitive detector, which was composed of a delay-line-type anode and Microchannel plates, was designed and constructed. The apparatus was installed into a vacuum chamber in the horizontal direction. The chamber was mounted as an endstation of the soft x-ray beamline BL6 of HiSOR in Hiroshima University. Synchrotron radiation was dispersed by a high-resolution monochromator and introduced into the chamber. Performance of the apparatus was tested using nitrogen molecule (N_2). Fragment ions (N^+, N^<++>) were produced after a photoexcitation of the nitrogen Is electron of N_2 and detected by the two-dimensional detector. The observed image for the fragment ions on the detector shows a concentric shape. This is quite reasonable based on the axial-recoil approximation in photodissociation of core-excited linear molecules, in which dissociation is much faster than molecular rotation.Next, the momentum images of N^+ and N^<++> were obtained after the N1s->σ^* resonant excitation by measuring the TOF spectra and position images on the detector. The obtained initial momentum vector of the fragment ion in dissociation is strongly distributed toward the direction of the electric vector of the incident light due to the Σ->Σ transition. Thus, the performance of the apparatus was satisfied sufficiently.Finally, the decay dynamics of core-excited CHF_3 molecule was investigated in the C K-edge. The peak of the kinetic-energy distribution of H^+ moves to high-energy side with the increase in excitation energy. At the C1s->3p resonant excitation, the kinetic-energy distributions of H^+ for (H^+-F^+) and (H^+-C^+) move to high-energy side in comparison with those for (H^+-CF_2^+) and (H^+-CF^+).