Dipole Spectrum of Water Vapor and Its Relation to the Energy Loss of Fast-Charged Particles

Abstract

Experimental and theoretical photoabsorption and photoionization cross sections and quantum mechanical sum rules are used to construct nonrelativistic dipole oscillator strength distributions for the following ''processes'' involving the ground state water molecule: total absorption, total ionization, total excitation to neutral species, and partial ionization to the ions H$sub 2$O$sup +$, OH$sup +$, and H$sup +$. These distributions are used to evaluate a number of dipole oscillator strength sums that are important in the radiation physics and chemistry of the water molecule and in the evaluation of the dipole properties of H$sub 2$O. Various parameters that occur in the Bethe--Born approximation for the total inelastic scattering cross sections that characterize the energy loss spectrum of fast-charged particles in water vapor are also evaluated and, where possible, compared with experimental results. The dipole oscillator strength sums are also used to evaluate the mean excitation energies for the stopping power and straggling of fast-charged particles in water vapor; I$sub 0$ = 70.8 eV and I$sub 1$ = 935 eV. (2 figs, 5 tables, 67 refs)