Extinction properties of ultrapure water down to deep ultraviolet wavelengths

We report on the optical extinction properties of the clearest ultrapure water measured so far within the wavelength interval between 181 nm and 340 nm (TOC level: 2.6 ± 0.7 ppb, specific conductivity: 0.055 μS cm−1). Our results extend the state-of-the-art extinction spectrum of ultrapure water by 15 nm towards shorter wavelengths and accurately resolve the ultraviolet extinction edge, allowing redefining a straightforward fitting function of the ultraviolet extinction of water (Urbach constant: 0.337 at 25 °C). The spectral distribution of our calculated Rayleigh scattering contribution shows a significantly better agreement with the experimental data than those reported in literature. The extinction temperature coefficient was determined in the range from 10 to 30 °C as a function of wavelength, showing significantly smaller values than those previously reported and being useful for noninvasively determining the temperature of ultrapure water samples.