Rhenium ionization energy

Another simple means of creating ions is a surface ionization source. This works effectively for species having low ionization energies, which in this work include atomic silicon and atomic transition metals. Typically, a rhenium filament resistively heated to about 2200 K is used. Silane or the vapors of a transition metal complex or salt are directed at the filament, where decomposition and ionization occur. It is generally believed that the electronic state distribution of the ions formed is in equilibrium at the filament temperature. This generally produces ground-state ions, e.g., exclusively Si+( P), with a distribution of spin-orbit levels associated with the filament temperature. 

The UPS spectra for these clusters reveal the general appearance of a 3-4 eV wide metal d band lying immediately below the Fermi level which is separated by 2-3 eV from an intense peak due to the CO 5intense peak at 3-4 eV below the 5a and l r features is due to the CO 4a levels. These spectra exhibit a remarkable qualitative similarity to the corresponding spectra of CO adsorbed on metal surfaces. More important for the present discussion is that they can be directly compared with the ionization energies obtained from theoretical calculations. For instance, the calculated spectra for a series of tetracobalt carbonyl clusters using the DV-Xa method have been compared with the He(I) UPS spectrum of [Co4(CO)i2]. [150] The transition state procedure [41] used in these calculations also accounted for the final state effects, that is, for the effects of orbital relaxation following the ionization process. This relaxation is typically about 2 eV for the valence orbitals of transition metal carbonyls and the calculated IP s compare well with the experimental ones. In a similar way, ruthenium, osmium, and rhenium carbonyl cluster UPS spectra have been calculated and reproduce the general trends and positions of the... 

The electrons are produced by heating a metallic filament (usually tungsten or rhenium) and accelerated by a voltage of 70 V that provides them a kinetic energy of 70 eV. Disposing of an international standard for the ionization energy allows a comparison of mass spectra recorded on different types of devices. Another benefit is access to databases that classify many thousands of mass spectra, which eliminates the need to interpret the spectra to identify the analytes. The databases are... 

An electron impact (El) ion source uses an electron beam, usually generated from a rhenium filament, to ionize gas-phase atoms or molecules. Electrons from the beam (usually 70 eV) knock an electron from a bond of the atoms or molecules creating fragments and molecular ions [366,534,535]. Several factors contribute to the popularity of El ionization in environmental analyses such as stability, ease of operation, simple construction, precise beam intensity control, relatively high efficiency of ionization, and narrow kinetic energy spread of the ions formed. 

A schematic of a prototypical El source is shown in Figure 2.1. The main body of the source is a metal block with holes drilled in it. Electrons are produced by heating to an incandescent temperature a thin filament (cathode) of rhenium wire, and are allowed to enter the ionization chamber through a slit. The applied potential difference (usually 70 V) between the filament and the ion-source block accelerates the electrons to the kinetic energy required. An electron trap (anode) placed just outside the ionization chamber opposite the cathode is held at a slightly positive potential with respect to the ion-source block. After traveling... 

Two different ionization methods are available in CGC-MS. namely, electron ionization (El) and chemical ionization (Cl). In electron ionizotion, the molecules are bombarded with electrons of 70 eV emitted from a rhenium or tungsten filament. A molecular radical ion is formed (M" -) with sufficient amount of energy accumulated in its bonds to dis.sociate into typical fragment ions, radicals, and neutral species. 

The relatively high electron affinity of UFe (Beauchamp, 1976a), 5 eV, has motivated studies of various uranium fluoride anions. Beauchamp produced UFfi" by surface ionization on a rhenium filament and studied its reactions with neutral llFg as a function of collision energy from 0 to 35 eV (Beauchamp, 1976a). It was determined that Eq. (7) occurs with an endothermicity of 2.7 0.2 eV ... 

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