Calibration of the pressure dependence of the <i>R</i>1 ruby fluorescence line to 195 kbar

The pressure dependence of the R1 ruby fluorescence line has been calibrated at 25 °C against the compression of NaCl. Pressures are determined using the Decker equation of state for NaCl. The dependence is linear to 195 kbar following the equation PNaCl=2.746(Δλ), where P is in kbar and Δλ in Å. The uncertainty in the value of the slope, dp/dλ, expressed in terms of a 95% confidence interval is 2.746±0.014 kbar Å−1. The coefficient of the quadratic term (Δλ)2 is not significantly different from zero; and the quadratic term makes indeed a negligible contribution to the fit. Taking into account the reported uncertainty associated with the Decker equation of state for NaCl, the value of the slope is 2.740±0.016 kbar Å−1 within a 95% confidence interval.