Protonated helium clusters

Shell-like Features and Charge Localization in Protonated Helium Clusters a Density Functional Study... 

The study of protonated helium clusters, therefore, challenges our ability to answer some, or all, of the following questions, to relate such answers to existing experiments and to provide reliable predictions for future experiments ... 

Shell-like features and charge localization in protonated helium clusters 103... 

When Rutherford allowed the radiation to pass between two electrically charged electrodes, he found that one type was attracted to the negatively charged electrode. He proposed that the radiation attracted to the negative electrode consists of positively charged particles, which he called a particles. From the charge and mass of the particles, he was able to identify them as helium atoms that had lost their two electrons. Once Rutherford had identified the atomic nucleus (in 1908, Section B), he realized that an a particle must be a helium nucleus, He2+. An a particle is denoted or simply a. We can think of it as a tightly bound cluster of two protons and two neutrons (Fig. 17.5). 

Penning ionization is a dominant reaction when nitrogen or neon is used in the DART source. Nitrogen or neon ions are effectively removed by electrostatic lenses and are not observed in the background mass spectrum. When helium is used, the dominant positive-ion formation mechanism involves the formation of ionized water clusters followed by proton transfer reactions. Negative-ion formation occurs by production of electrons by Penning ionization or by surface Penning ionization ... 

Another ionization process that is the main process when helium is used as the gas is proton transfer. This type of ionization occurs when metastable helium atoms react with water in the atmosphere to produce ionized water clusters that can protonate the sample molecule, leading to the protonated molecule. 

In helium, in which this interaction is weak due to its low polarizability, the proton-ated primary and tertiary ions are affected similarly (and weakly) by the drift gas molecules. On the other hand, in air, the neutral molecules, especially nitrogen, cluster preferentially with the localized charge on the primary amines, leading to larger electrostatic interactions, rather than with the delocalized and shielded charge of the tertiary amine ions. Thus, a difference in the mobility in air of isomeric ions should arise, as is, indeed, observed. 

De Paz et have described recently a new technique with which cluster dissociation energies can be determined. Their study dealt with the proton hydrates H (H20) . The proton hydrates were produced by electron irradiation of water vapor in the 0.1-3-Torr range in the first ion source of a tandem mass spectrometer. The ion source of the second stage served as collision chamber and was filled with helium. Ions H (H20)fc formed by collisions of the primary H (H20) with He were detected with the second mass spectrometer. The energy required for the process... 

Figure 7.6 Proton-transfer reaction between 1-naphthol and ammonia with helium as carrier gas. Transients recorded in pump-probe experiments on the proton-transfer reaction between 1-naphthol (ROH) and ammonia (B) in clusters ROH.. B with n = 0 to 6. From Figure 7 of Ref. [6,a].

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