Photoionization threshold

Herrmann A, Leutwyler S, Schumacher E and Woste L 1978 On metal-atom clusters IV. Photoionization thresholds and multiphoton ionization spectra of alkali-metal molecules Hel. Chim. Acta 61 453... 

TABLE II. Photoionization Thresholds in Gaseous Benzene and Its Derivatives Obtained by Mass Spectrometry... 

It will be seen from Table II that the energy of the second photoionization threshold exceeds the first by a nearly constant value, equal to about 1.1 to 1.4 e.v. The energy of the third threshold exceeds the first for all the compounds studied by a nearly constant value of 2.4 0.2 e.v. 

Figure 5-17. Photoionization threshold energy spectra for DABCO(CH3OCH3) and DABCO(TEA)i (2p3s) Rydberg state. Excitation is at the cluster first observed origin transition. The values of At represent the time delay between the excitation laser and the ionization laser.

One can therefore, in general, not separate the relaxation and shake up effects induced by the hole from the corresponding effects induced by the photoelectron. These considerations are particularly important in the photoionization threshold region where the speed of the photoelectron is relatively low. 

L3-M1M1) = 34.87 eV. However, as the photoionization threshold is approached one can note rather pronounced structures in the parameter at... 

A more precise value is available from the photoionization measurements of Walter et al. (6), who measured the photoionization threshold the process. for... 

Dibeler and Liston ( ) reported the photoionization threshold for the process CH CN... 

Chupka and Lifshitz (1 ) have obtained the photoionization threshold for CH2 from CHg as 15.09 0.03 eV. Combining this... 

Dibeler and Liston (, 4) have studied a series of cyanogen compounds and obtained their enthaplies of dissociation from photoionization threshold measurements. The values below are obtained from the halogen ion threshold measurements, except for HCN which is from the CN threshold measurements. The value below is calculated using the IP from CNCl measurements (3). 

Figure 12. Relative rate constants (left-hand scale, data points) as a function of cluster size for Dj chemisorption onto iron, vanadium, and niobium clusters. Activation energies, derived from cluster photoionization thresholds [Eq. (21)], are indicated by solid line and right-hand scale. See text for definition of parameters.

For the determination of enumerated energy characteristics, use may be made (in a particular combination) of the following quantities measured by experiment threshold of photo-induced and thermal electron emission from metal to solution and from solution to vapour phase solvated electron photoionization threshold ... 

Fig. 6.41. (a) PTI spectrum at LHeT of a GaAs sample with Nd — Na = 2 x 1013 at cm-3 showing the Is — 2p transition for three different impurities. The dotted, bar indicates the average photoionization threshold at zero field, (b) PTI spectrum of the same sample under a magnetic field of 6.3 T showing the dominant Is — 2pm= i component and the weak Is — 2pm=o component. The attributions to specific impurities and the FWHMs (cm-1) are indicated (after [33])... 

Examination of the photoionization thresholds and absorption cross sections for atmospheric constituents shows that the solar radiation capable of producing ionization is primarily absorbed by O2, N2, NO, and 0. Table 7.2 presents the photoionization thresholds for various... 

Ionization potentials of atoms are usually obtained by the determination of a photoionization threshold or more accurately by the observation of long Rydberg progressions. With the exception of a few of these elements with simple spectra, obtaining such measurements for lanthanides and actinides is difficult if not impossible by conventional spectroscopy. Therefore, very accurate ionization limits were not available for the majority of these elements.( 6)... 

The Rydberg series and photoionization thresholds obtained have permitted the accurate determination of ionization limits for uranium, (1) neptunium, and ten lanthanides. Q)... 

The photoionization threshold from one or more excited levels of the atom under study was determined first using the excitation schemes of Fig. 2. This involved scanning a... 

Because the ionization potentials obtained from Rydberg convergence limits are much more accurate, the photoionization thresholds served mainly to limit the search range to find Rydberg series. The praseodymium threshold value is an exception because no Rydberg series were obtained for that element. The photoionization threshold of 5.464+0 012 eV t ie only experimental value available for praseodymium. 

Janes et al.(2) were the first to apply multistep photoionization to the study of uranium. Their result for the photoionization threshold of 6.187(2) eV is in good agreement with the photoionization result of 6.1912(25) eV obtained by Solarz et al.(D (Throughout this paper, numbers in paranthesis following a numerical value indicate the uncertainty in the last digit of the number.)... 

Figure 3. Photoionization threshold spectra for neodymium. The excitation scheme used in each case is shown on the figure. The scanned laser wavelength calibration is shown at the top of each spectrum. In (a) the 20 300.8 cm 1 level is populated and in (b) the 21 572.6 cm 1 level is populated. The threshold wavelengths indicated yield the same ionization limit value of 5.523 eV. The arrows labeled R. L. indicate the position of the Rydberg convergence limit (3).

Figure 4. Neptunium photoionization threshold spectrum. The excitation scheme is shown at the left. The threshold at 4593 A is marked by the onset of very strong autoionization peaks. It yields an ionization potential of 50 518 cm 1...

Table I. Representative stepwise laser photoionization threshold results...

The photoionization threshold values listed in column 4 are all lower by some 0.002 to 0.005 eV (15-30 cm l). Similar differences were found in uranium and neptunium and remain unexplained. Electric fields from the ion optics (field ionization) and collisional effects are possible explanations. In all cases, the Rydberg convergence limits are the most accurate and they are the preferred values. 

The spectra of atoms are characterized by a set of bound Rydberg states below the photoionization threshold for excitations in the continuum " The Rydberg states become very weak in molecules and disappear in condensed systems. Review papers on x-ray absorption spectra for atoms and molecules are available and these spectra will not be discussed here. 

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