Volume 122, Issue 14, 08 April 2005
Index of content:
122(2005); http://dx.doi.org/10.1063/1.1890885View Description Hide Description
We present a new experimental approach, in which anion photodetachmentspectroscopy is recorded with electrons of fixed kinetic energy. This approach circumvents some shortcomings of the zero electron kinetic energy method. Our method is based on a modified magnetic bottle photoelectron spectrometer (MBPES). A tunable laser is used to detach electrons from mass selected anions, drifting collinearly with the 40 cm MBPES drift tube. To avoid Doppler broadening, a low voltage pulse removes the velocity component of anions from the detached electrons. Spectra are recorded by collecting the wavelength dependence of electron-signal at a predetermined TOF window, corresponding to a specific electron-kinetic energy. We call this approach PEACE, denoting photoelectron action spectroscopy at constant kinetic energy. Our best resolution is 0.65 meV for 1.5 meV electrons. We present a PEACE spectrum of together with the corresponding simulated theoretical spectrum. The method is similar in resolution and data collection rates to the slow electron velocity map imaging technique recently introduced by Neumark and co-workers.
122(2005); http://dx.doi.org/10.1063/1.1897374View Description Hide Description
The hard/soft-acid/base (HSAB) principle indicates that hard acids prefer binding to hard bases (often formingbonds with substantial ionic character) while soft acids prefer binding to soft bases (often formingbonds with substantial covalent character). Though the HSAB principle is a foundational concept of the modern theory of acids and bases, the theoretical underpinnings of the HSAB principle remain murky. This paper examines the exchange reaction, wherein two molecules, one the product of reacting a hard acid and a soft base and the other the product of reacting a soft acid with a hard base, exchange substituents to form the preferred hard–hard and soft–soft product. A simple derivation shows that this reaction is exothermic, proving the validity of the HSAB principle. The analysis leads to the simple and conceptually appealing conclusion that the HSAB principle is a driven by simple electron transfer effects.
122(2005); http://dx.doi.org/10.1063/1.1893605View Description Hide Description
Switching of molecular chirality under photo-irradiation was studied in a cobaloxime complex crystal. Excitation of the transition of the Co(III) ion appeared to be much more effective in inducing the chirality change than excitation of the ligand-metal charge transfer band although the latter is more effective in breaking the Co–C bond that initiates the chirality switching. The chirality change versus irradiation time showed a steplike behavior suggesting that chirality switching of molecules occurred in correlation with their nearest neighbors.