Threshold-photoelectron photoion coincidence (TPEPICO) spectra of CH4 have been observed with synchrotron radiation at the excitation to the 2A1 (ν1=0−3) ionic states as well as to the 4pt2 Rydberg (ν1=0−4) states. In all the TPEPICO spectra observed, the CH+3 band shape was almost rectangular, which suggests that the translational and internal energy distributions of CH+3 are very narrow. The total kinetic energy releases (KERs) have been estimated from the CH+3 band shape. As a result, it was found that the CH+3 species were in an electronically excited state. There was a narrow distribution of the total KERs and similarity in the TPEPICO CH+3 band shapes between the spectra at the 2A1 ionic state and the 4pt2 Rydberg state excitations, which led to the conclusion that the Rydberg electron is just a spectator and the dissociation of the core ion plays an important role in dissociation through the 4pt2 Rydberg state. Similar results have also been obtained for CH+2 and CH+ productions. However, on the other hand, an H+ fragment has been observed only at the 2A1 state excitation. It showed a band with a long tail in the slower flight time region. The total average KERs and the decay rates have been estimated from band shape simulation. From these results, it has been found that a dissociation limit of the H+ ion exists just below the 2A1 ionic state. The dissociation mechanisms through the 4pt2 Rydberg state have been discussed in detail in comparison with those of the 2A1 ionic state.

A new crossed molecular beam apparatus with a high-resolution ion imaging detector is described. Two pulsed supersonic molecular beams are crossed at right angles in a vacuum of 10−7 Torr. The collision region is irradiated with a tunable laser pulse that ionizes the scattered particles state selectively. The generated ions are accelerated by stacked electrodes in a two-dimensional (2D) space focusing mode that increases the velocity resolution of the apparatus. A cylindrical hexapole deflector is placed in the middle of the time-of-flight mass spectrometer to compensate the center-of-mass velocity of the ions and to direct them to the center of the 2D imaging detector. Real-time image processing of the charge coupled device camera signal eliminates blurring of the image detector. The performance of the apparatus was examined by observing the inelastic scattering of NO+Ar at a collision energy of 66 meV. The observed multiple rainbow peaks clearly demonstrate the high performance of the apparatus.

We demonstrate the simultaneous production of spin-polarized ions/electrons using two-color, two-photon ionization of laser-ablated metallic atoms. Specifically, we have applied the developed technique to laser-ablated Sr atoms, and found that the electron-spin polarization of Sr+ ions, and accordingly, the spin polarization of photoelectrons is 64%±9%, which is in good agreement with the theoretical prediction we have recently reported [T. Nakajima and N. Yonekura, J. Chem. Phys. 117, 2112 (2002)]. Our experimental results open up a simple way toward the construction of a spin-polarized dual ion/electron source.

Articles you may be interested inElectron-spin polarization of photoions produced through photoionization from the laser-excited triplet state of Sr Resonance enhanced multiphoton ionization of the hydrogen halides: Rotational structure and anomalies in Rydberg and ion-pair states of HCl and HBrWe propose two realistic schemes for producing electron spin-polarized alkaline-earth ions. One of the schemes is based on one-photon resonant two-photon ionization via fine structure manifolds of triplet states, while the other is based on one-photon resonant one-photon ionization. For both schemes we find that the ionization must take place from a triplet state to produce spin-polarized photoions. Photoions produced from a singlet state are always unpolarized regardless of the laser polarization and a magnetic sublevel from which ionization takes place. We carry out specific analysis for both schemes with Sr atoms, and find 85%-90% and 66% polarizations for the former and the latter schemes, respectively, if the wavelengths and polarizations of lasers are judiciously chosen. In particular, if all the produced photoions are in the ground s state, we find an exact one-to-one correspondence between the spin-polarization of photoions and ejected photoelectrons.

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