Deuterium and Sodium Quadrupole Interactions in Sodium Hydroxide. The Monoclinic Phase

Abstract

The temperature dependence of the 23NaOH Pure Quadrupole Resonance Frequency has been studied from 77 K to 550 K and shows a change in slope and a discontinuous change in frequency of 6 ± 2 kHz at the orthorhombic to monoclinic phase transition at 505 K At 292 K the 23Na NQR frequency is 1.778 ± 0.001 MHz, η < 0 .04. The temperature dependence of the deuterium quadrupole coupling was fit to a librating molecule model between 293 K and 570 K (QCC = 245 ± 2 kHz, η = 0.05 ± 0 .0 1 at 293 K) and confirms that the frequency of the libration decreases in the high temperature monoclinic phase. X-ray studies indicate that down to 10 K there are no further phase transitions in NaOH. On the other hand, it is now known that NaOD, orthorhombic at room temperature, monoclinic at high temperature, suffers another transition at 160 K to yet another monoclinic phase.