Photoionization yield

Photoionization can also access excited electronic states of the ion that are difficult to study by optical methods. The photoionization yield of FeO increases dramatically 0.36 eV above the ionzation energy. This result corresponds to the threshold for producing low spin quartet states of FeO. These states had not been previously observed, as transitions to them are spin forbidden and occur at inconveniently low energy. Because the FeO + CH4 reaction occurs via low spin intermediates, accurately predicting the energies of high and low spin states is critical. 

Figure 4. Fe cluster ionization thresholds as a function of cluster size, as determined by photoionization yield measurements using tunable UV/VUV laser radiation.

Photoionization yields even more accurate results ( 0.05 eV) than the electron monochromator. [86] In any case, the half width of the electron or photon energy distribution becomes small enough to detect detailed structural features of the... 

The early work on the photolysis of water was in the gas phase employing one photon. The branching ratio of the photodissociation into H + OH and H2 + O was reported by McNesby et al. [28] as 3 1 at a photon energy of 10.03 eV. Ever since, that ratio has been consistently revised in favor of the H + OH reaction with the final result of Stief et al. [29] giving 0.99 0.01 for 6.70-8.54 eV photon energy and 0.89 0.11 for the interval 8.54-11.80 eV. In the absence of direct determination these ratios often are assumed valid in the liquid phase. In the early work of Sokolev and Stein [30], mainly the photodissociation quantum yield in liquid water was measured, but a small photoionization yield of -0.05 was attributed to the process... 

Prof. Schlag ( ZEKE Spectroscopy, this volume) has introduced a new sequential technique of ZEKE spectroscopy In the first step, a negative ion M is photoionized, yielding the neutral core M of the excited Rydberg state of the anion M. In the second step, M is further photoionized, yielding the cationic core M+ of the excited Rydberg state of the neutral molecule M. The overall sequence is thus... 

Barbouti A, Doulias P-T, Zhu B-Z, Frei B, Galaris D (2001) Intercellular iron, but not copper, plays a critical role in hydrogen peroxide-induced DNA damage. Free Radical Biol Med 31 490-498 Bartels DM, Crowell RA (2000) Photoionization yields vs energy in FI2O and D2O. J Phys Chem A 104 3349-3355... 

The Ar(3P(, Pt) levels are 11.623 and 11.827 eV, respectively, above the ground (1S) level. The lifetimes are 8.4 and 2.0 nsec (33), respectively. The Ar(3P,1 Pj) states are formed by absorption of the Ar resonance lines at 1067 and 1048 A. In the 1 to 100 mtorr concentration range the lifetime of Ar(3P, P() atoms is of the order of 10 /tsec [Hurst et al. (494)], which is 1000 times as long as that of isolated atoms because of imprisonment of resonance radiation. If the ionization potential ofa molecule is below 11.6 eV, it is possible to increase the photoionization yield (sensitize) by adding Ar to the sample. The increase of the ionization yield is caused by collisional energy transfer between Ar(3P, Pi) atoms and the molecule before the excited atoms return to the ground state by resonance emission. Yoshida and Tanaka (1065) have found such an increase in the Ar propane, and Ar-ammonia mixtures when they are excited by an Ar resonance lamp. Boxall et al. (123) have measured quenching rate constants for Ar(3P,) atoms by N2) 02, NO, CO, and H2. They are on the order of the gas kinetic collision rate. 

The ability of micelles to enhance photoionization yields of hydrophobic molecules was demonstrated in the early 1970s. Thus, the photoionization yields of pyrene [59], phenothiazine [60] and tetramethylbenzidine [61] cations increased when these molecules were encapsulated in anionic micelles. The effect was attributed to efficient escape of electrons from the geminate charge-separated species formed within the micelle, which is accelerated by the anionic interface. The negative micellar surface imposes an electrostatic barrier between the cations, which remain with the micelle, and the aqueous electron in the bulk water phase, thus increasing the lifetimes of the photoredox products. 

The reasons for the divergent effects of surface charge on TMB and ZnTPP photoionization yields in vesicular suspensions are unknown. Experimentally determined photoionization yields are complex quantities, which include as elementary processes primary ionization cross-section terms, dry electron escape probabilities, relatively complex electron hydration processes and recombination of various hy-... 

The dependence of the gadolinium photoion yield at the absorption of the autoionization resonance of 6133.5 A on the pulsed-energy density, E3, of the ionizing laser. Laser band width 0.03 cm 1 (5). 

The photoionization yields of trimethylamine, dipropylamine, di-isopropylamine, and tetramethylene sulphide at 147 nm have been determined as 0.38, 0.46, 0.096, 0.15, and 0.10 respectively, and their use as actinometers at this wavelength has been advocated.94 Photoionization and ion-molecule reactions in propyl-, ethyl-, diethyl-, and triethyl-amines have also been discussed,95 and striking differences between the vapour-phase and solution-phase photochemical 88... 

Fig. 11. Photoion yields of Kr" " (atom) Kr2" at various average cluster-sizes N), and the total electron yield of solid Kr (top) in the Kr 3c<5/2 regime (cf. Ref. 72). Further details are described in the text.

Fragmentation of core excited clusters becomes already evident from mass spectra, where the mass distribution is concentrated at much smaller masses than estimated from the average cluster-size N) (cf. Fig. 9). In addition, it is shown in Fig. 11 that photoion yields of mass-selected cluster fragments reflect changes in electronic structure as a function of (N). However, these results give no specific information on the mechanisms that lead to stable product ions. 

Several autoionization features observed In a plot of the photoionization yield of PHJ from PH2 (obtained from the PH3 + H reaction) between 1259 and 1113 A (9.85 to 11.1 eV) probably are members of Rydberg series converging on the excited states a Bi and A B of the PHJ ion (see p. 95). The bending vibration apparently leads to a vibrational structure (for a more detailed discussion, see the original paper) [55]. 

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