This article reviews our recent work on photo-stimulated ion desorption (PSID) from molecules condensed at low temperature. We have used electron-ion coincidence (EICO) spectroscopy combined with synchrotron radiation. The history and present status of the EICO apparatus is described, as well as our recent investigations of condensed <$E roman {H sub 2 O}>, <$E roman NH sub 3>, <$E roman {CH sub 3 CN}>, and <$E roman {CF sub 3 CH sub 3}>. Auger electron photoion coincidence (AEPICO) spectra of condensed <$E roman {H sub 2 O}> at the O:1s ionization showed that <$E roman H sup +> desorption was stimulated by O:KVV Auger processes leading to two - hole states (normal- Auger stimulated ion desorption (ASID) mechanism). The driving forces for <$E roman H sup +> desorption were attributed to the electron missing in the O - H bonding orbitals and the effective hole-hole Coulomb repulsion. The normal ASID mechanism was also demonstrated for condensed <$E roman NH sub 3>. The <$E roman H sup +> desorption at the <$E 4a sub 1~symbol М~roman O(N):1 s> resonance of both condensed <$E roman {H sub 2 O}> and condensed <$E roman NH sub 3> was found to be greatly enhanced. Based on the AEPICO spectra the following four-step mechanism was proposed: (1) the <$E 4a~symbol M~1s> transition, (2) extension of the HO - H (<$E roman {H sub 2 N~-~H}>) distance within the lifetime of the <$E (1s) sup -1 (4a1) sup 1> state, (3) spectator Auger transitions leading to <$E roman {(valence) sup -2}~(4a1) sup 1> states, and (4) <$E roman H sup +> desorption. The enhancement of the <$E roman H sup +> desorption yield was attributed to the repulsive

potential surfacof the <$E (1s)~-~1(4a sub 1) sup 1> state. At the <$E 3p ~symbol M~ O:1s> resonance of condensed <$E roman {H sub 2 O}>, on the other hand, the <$E roman H sup +> yield was found to be decreased.The AEPICO spectra showed that the <$E roman H sup +> desorption was stimulated by spectator Auger transitions leading to <$E roman {(valence) sup -2} (3p) sup 1} states. The decrease in the <$E roman H sub +> yield was attributed to a reduction in the effective hole-hole Coulomb repulsion due to shielding by the <$E 3p> electron. Photoelectron photoion coincidence (PEPICO) spectra of condensed <$E roman {H sub 2 O}>. The <$E roman H sup +> desorption from condensed <$E roman {CH sub 3 CN}> was also investigated. In a study of condensed <$E roman {CF sub 3 CH sub 3}> using PEPICO spectroscopy, site-specific ion desorption was directly verified; that is, <$E roman H sup +> and <$E roman CH sub 3 sup +> desorption was predominant for the C:1s photoionization at the -<$E roman CH sub 3> site, while <$E roman {C sub 2 H} sub n sup +>, <$E {roman CFCH} sub m sup +>, and <$E roman CF sub 3 sup +> desorption was predominantly induced by the C:1s photoionization at the -<$E roman CF sub 3> site. These investigations demonstrate that EICO spectroscopy combined with synchrotron radiation is a powerful tool for studying PSID of molecules condensed at low temperature.

Індекс рубрикатора НБУВ: В368.3 + В369

Рубрики:

Фізика низьких температур

Фізика конденсованих середовищ

Шифр НБУВ: Ж14063 Пошук видання у каталогах НБУВ 

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