Absolute photoabsorption cross sections for H2O and D2O from λ 180–790 Å

Abstract Absolute photoabsorption cross sections for H 2 O and D 2 O have been measured photoelectrically from λλ 180 to 790 A using synchrotron radiation. The cross sections increase smoothly with wavelength to ∼λ610 A, with both H 2 O and D 2 O displaying a broad absorption band extending above a nearly linear background from λλ 400 to 490 A. The continuum has a maximum of ∼ 22.5 Mb at λ 640 A. Above λ 615 A, superimposed on the continuum, a diffuse structure appears which is similar to the vibrational structure of the 2 B 2 states of H 2 O + and D 2 O + as observed in photoelectron spectra. The structure is believed to arise from excitation of a 1 b 2 electron to the vibrational levels of a Rydberg orbital with n ∗ ≈ 2.64.

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