Ionization water vapor

When averaged over the distribution of energy loss for a low-LET radiation (e.g., a 1-MeV electron), the most probable event in liquid water radiolysis generates one ionization, two ionizations, or one ionization and excitation, whereas in water vapor it would generate either one ionization or an excitation. In liquid water, the most probable outcomes for most probable spur energy (22 eV) are one ionization and either zero (6%) or one excitation (94%) for the mean energy loss (38 eV), the most probable outcomes are two ionizations and one excitation (78%), or one ionization and three excitations (19%). Thus, it is clear that a typical spur in water radiolysis contains only a few ionizations and/or excitations. 

Following Platzman (1967), Magee and Mozumder (1973) estimate the total ionization yield in water vapor as 3.48. The yield of superexcited states that do not autoionize in the gas phase is 0.92. Assuming that all of these did autoion-ize in the liquid, we would get 4.4 as the total ionization yield. This figure is within the experimental limits of eh yield at 100 ps, but it is less than the total experimental ionization yield by about 1. The assumption of lower ionization potential in the liquid does not remove this difficulty, as the total yield of excited states in the gas phase below the ionization limit is only 0.54. 

Cole [52] measured the W value in air for electron energies from 5 to 20 eV, while the electrons were completely absorbed in the ionization chamber. Later, Combecher [53] extended the measurements of W E) to several gases including water vapor. Fig. 6 shows the variation of W E) with electron energy in water vapor, as measured by Combecher,... 

Figure 4 Doubly differential cross sections for the ionization of water vapor by 1-keV electron impact. (From Ref. 38.)...

Figure 16 Ionization of water vapor by 150-keV H° particles. The e and H° impact data are from Refs. 38 and 67, and the parameters for the Rudd model are from Ref. 36. The dotted line is discussed in the text under the section on effective charge.

Figure 18 Ionization of water vapor by 2-MeV He and ions. The dashed line is an estimate of the contribution of target ionization by He obtained by interpolation from regions beyond the vicinity of electrons contributed by electron loss by the He ion. (From Ref. 68.)...

Inelastic cross sections for ionizations and excitations were compiled for low- and high-energy electrons. The experimental ionization cross sections for water vapor in the energy range of 10 eV to 10 keV [177-181] were least-squares fitted as shown by a solid line in Fig. 7 using a model function ... 

Figure 8 Total cross sections for ionization, excitation, and elastic scattering of electrons in water vapor in the energy range of 10 eV to 10 MeV.

Figure 11 Total cross sections due to proton (left) and alpha particle (right) impact on water vapor. Total ionization cross sections were obtained by fitting polynomial functions to the experimental data [198-200]. The curve for excitation was assumed to be the same between protons and alpha particles. Elastic scattering was evaluated by the classical mechanics trajectory calculations [Eqs. (16) and (17)].

Figure 15 Total ionization cross sections due to dressed ion impact on water vapor. Cross sections for and He were adjusted to reproduce stopping powers for the lower energy protons and alpha particles. (Experimental data from Refs. 200, 213, and 217.)...

An opposite result has been obtained in Ref. 14, where, using the Monte Carlo method, the authors made a comparative study of the influence the state of aggregation of water has on yields of ionized and excited states and on the way electron energy is absorbed. According to Ref. 14, with transition from vapor to liquid, the number of ionizations induced by a fast electron increases, while the value of Wt (at Ee = lOkeV) lowers from 30.0 to 24.6 eV. Both in liquid water and in water vapor the yield of ions exceeds that of excited molecules. In our study,143 which we have made in collaboration with Sukhonosov, we simulated the primary stage of water radiolysis and have obtained a somewhat different result. 

Yields of Ionized gjon and Excited g c States and the Values of W, in Liquid Water and in Water Vapor Irradiated by 10-keV Electrons... 

A hand-held field PID consists of an air uptake pump, an ultraviolet (UV) ionization lamp, a photo multiplier, and a readout device. The air drawn in by the pump passes along the lamp, where organic compounds are ionized with UV light. The resultant current is converted into a signal proportional to the number of ionized molecules. The UV lamp is calibrated with a standard (isobutylene in air), and the readout device provides the vapor concentrations in parts per million-volume (ppm-v). UV lamps are sensitive to the presence of moisture high water vapor content in air will suppress their ionizing action. Some PID models have a moistureabsorbing filter that can be attached to the instrument s inlet. 

Moderately selective to aromatic compounds when a lamp with ionization energy of 10.2 eV is used Photoionization detector Volatile aromatic hydrocarbons (EPA 8021) —Many non-aromatic volatile organic compounds have a response on a 10.2 eV lamp. —Higher energy lamps (11.7 eV) ionize a wide range of volatile compounds. —Water vapor suppresses response. 

Dutuit, O., Tabche-Fouhaile, A., Nenner, I., Frohlich, H., and Guyon, P.M. (1985). Photodissociation processes of water vapor below and above the ionization potential, J. Chem. Phys. 83, 584-596. 

PPX films containing PbO nanocrystals also show increase in their conductivity under action of small quantities of ammonia and ethanol vapors from gaseous environment [89, 102, 103]. This effect takes place in the presence of water vapors only and so, most probably, is due to the formation of ionized or highly polarized molecular complexes NH3 H2O and C2H5OH H2O. The responses of conductivity to ammonia and ethanol are also reversible the film conductivity returns to its initial value after the removal of these substances from the surrounding atmosphere. 

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