Proton tunnelling frequencies in ammonium salts from spin-lattice relaxation

Abstract

Proton reorientation tunnelling in many NH4+salts gives a frequency independent minimum in both T1and T1 rhoat the transition to classical relaxation at about 40-70K. The average tunnel frequency is approximately: f1approximately=4*109Ti1( rho )min,(Hz when T1or T1 rhois in s). Tunnel frequencies are derived from T1and T1 rhomeasurements on NH4ClO4, cubic and trigonal (NH4)2SiF6, (NH4)2SnCl6, (NH4)2Ce(NO3)6, (NH4)2Cr2O7and literature data, and compared with tunnel frequencies calculated from barrier heights.