Pure nuclear quadrupole resonance of ionic halides, 1

The 79Br-NQR spectra of anilinium bromide, C6H5NH3+Br-, of anilinium-d3 bromide, C6H5ND3+Br-, and of anilinium-d5 bromide, C6D5NH3+Br-, have been investigated in the temperature range 77<=T/K<=350. The three compounds show an order-disorder phase transition near room temperature. The respective transition temperatures have been determined as 296.9 K (C6H5NH3+Br-), 291.5 K (C6H5ND3+Br-), and 297.6 K (C6D5NH3+Br-). The large value of the 79Br-NQR frequency (ν=17.780 MHz at 77 K for C6H5NH3+Br-) and the large 1H-2D isotopic shift of this frequency (asymptotically equals 400 kHz at 77 K by deuteration of the NH3+-group) have been interpreted in terms of hydrogen bonding N-H--Br-. The state of order in the high temperature modification is discussed in the light of the 79Br-NQR spectrum. The 79Br-NQR frequency of the Br- ion in the low temperature modification is related to the change in the monoclinic angle β and to the temperature dependence of the order parameter s proportional to ((T sub(c) - T)/T sub(c))sup(1/3). (auth.)