Quadrupole echoes and the 127I nuclear hexadecapole interaction in KI

Abstract

A quadrupole echo method for searching for the nuclear hexadecapole interaction (HDI) is described. A sequence of three radio frequency pulses applied at times 0, τ, and nτ (n>1) gives a simple pattern of nuclear spin (5)/(2) echoes when only the nuclear Zeeman and quadrupole interactions are present. Calculations for n=2.5, 3.0, 4.0, and 5.0 show that these patterns undergo an elaborate change when the HDI is also present and that these echo patterns are unique to the HDI. Three pulse echoes were used to search for the 127I HDI in a single crystal of KI but, for this sample, a two pulse sequence was found to be more effective. For KI, 2.8 kHz is the estimated magnitude of the 127I hexadecapole coupling constant, eHV(4)/h, where eH is the 127I electric hexadecapole moment and V(4) is a fourth derivative of the electrostatic potential at the nuclear site. This is the smallest HDI measured in a solid so far.