Mitsuru Nagasono, Kazuhiko Mase, Shin-ichiro Tanaka, and Tsuneo Urisu
[Chem. Phys. Lett., 298, 141-145 (1998)]
Desorption of H+ from condensed H2O at 80 K, induced by O 1s ionization, is studied using Auger electron-photoion coincidence spectroscopy. It is found that H+ desorption is induced by the O KVV Auger transitions and that the desorption probability is enhanced when holes are created at O-H bonding orbitals.
Kazuhiko Mase, Mitsuru Nagasono, Shin-ichiro Tanaka, Tsuneo Urisu, Eiji Ikenaga, Tetsuji Sekitani, and Kenichiro Tanaka
[J. Chem. Phys., 108, 6550-6553 (1998)]
The Auger electron photoion coincidence (AEPICO) technique has been applied for the study of H+ desorption induced by resonant excitations of O 1s of condensed H2O. The peak positions of the AEPICO yield spectrum at the 4a1<--O 1s resonance (hƒË=533.4 eV) are found to correspond to spectator-Auger transitions leaving (O 2s)-2(4a1)1, (O 2s)-1(O 2p)-1(4a1)1, and (O 2p)-2(4a1)1 states. The H+ AEPICO yield is greatly enhanced at 4a1<--O 1s while it is suppressed at 3p<--O 1s (hƒË=537 eV) as compared with that at the O 1s ionization (hƒË=5560 eV). On the basis of these results, the ultrafast ion desorption mechanism is suggested to be favorable for the H+ desorption at 4a1<--O 1s, that is, the repulsive potential energy surface of the (O 1s)-1(4a1)1 state is responsible for the H+ desorption. For H+ desorption at 3p<--O 1s, a spectator-Auger stimulated ion desorption mechanism is concluded to be probable. The suppression of the H+ AEPICO yield is ascribed to the reduction of the hole-hole repulsion due to the shield effect of the 3p electron. These results demonstrate the power of the AEPICO technique to clarify the mechanism of ion desorption induced by core-electron excitations.
S. Tanaka, K. Mase, M. Nagasono, and M. Kamada
[J. Electron Spectrosc. Relat. Phenom., 92, 119-122 (1998)]
Desorption of F+ induced by core-level excitation with synchrotron radiation has been invesdgatcd on the CaF2(1 1 1) film produced on Si(1 1 1). The ion yield is proportional to electron yield in the region of the Ca-2p edge, while an enhaucement of the ion yield is observed at the photen energy for the F-1s core-exciton. The peak corresponding to the F-1s excitation observed in the ion yield is shifted from that in the electron yieid by about - 1.2 eV, which is predominantly ascribed to the change in the Madelung potentia] at the surface. The electron-ion coincidence study shows that the F+ desorption is directly stimulated via a decay of the F-1s surface core-exciton, while secondary-electron stimulated desorption is the predominant process after the creation of Ca-2p hole.
I. Shimoyama, T. Mochida, Y. Otsuki,
H. Horiuchi, S. Saijyo, K. Nakagawa, M. Nagasono, S. Tanaka, and K. Mase
[J. Electron Spectrosc. Relat. Phenom., 88-91, 793-799 (1998)]
C-H dissociation is known to be responsible for the formation of radiation damage of hydrocarbon crystals such as color centers or radicals. Recently, Auger electron photoion coincidence (AEPICO) spectroscopy has allowed us to get detailed information on microscopic processes of radiation damage, because AEPICO spectroscopy can pick up only the fundamental processes, excluding effects due to secondary electrons, In this work, in an attempt to study which electronic state is responsible for the C-H bond dissociation, AEPICO spectra of benzene solid were measured at 80 K as a function of photon energy. AEPICO measurements were examined at three photon energies, i.e. 285 eV (ƒÎ*(e2ƒÊ<- 1s), 287 eV (ƒÐ*(C-H) <- 1s), and 430 eV (ionization <- 1s). Relative magnitudes of the AEPlCO yield Y(hƒË), which reflects the C-H dissociation yield, were estimated by dividing AEPICO signals with intensities of Auger electron yield, Experimental results showed that Y(287 eV)/Y(430 eV) = 1 , whereas Y(28S eV)/Y(430 eV) = 0.13. A relation between the small value of Y(285 eV)/ Y(430 eV) with the small values of the radiation damage yield ƒÅ(hƒË) near 285 eV is discussed. In that case, ƒÅ(near K edge)/ƒÅ(over K edge) = 0.1 -0.3 [5] [A. Kimura, K. Nakagawa, K. Tanaka, M. Kotani, R. Katoh, Nucl. Instr. and Meth. in Phys. Res. B91 (1994) 67].
Tetsuji
Sekitani, Eiji Ikenaga, Hideki Matsuo, Shin-ichiro Tanaka, Kazuhiko Mase,
and Kenichiro Tanaka
[J. Electron Spectrosc. Relat. Phenom., 88-91, 831-836 (1998)]
Photon stimulated ion desorption (PSID) of condensed acetonitrile molecules induced by carbon and nitrogen core excitation has been examined to elucidate the Auger process following resonant core cxcitation and the ion desorption mechanism related to this Auger process using total electron yield, total ion yield, resonant Auger electron spectra. Resonant Auger electron spectra show a strong dependence on the character of excitation, In particular, these Auger spectra are drastically changed between the carbon 1s to the ƒÎ*CN excitation and that of the C-H* excitation. The spectrum of the total ion yield divided by the total electron yield shows that the desorption efficiency is largely increased at the resonant excitation of carbon 1s electron in the CH3 group to C-H* orbital. The results of the resonant Auger spectra and the Auger electron-photoion coincidence (AEPICO) measurements at various resonant excitations are discussed in relation to the bonding/anti-bonding character and localized character of the excited state and the Auger final state.