NQR frequencies in 3&dichlorophenolare investigated in the temperature range 77 K to room temperature. Two resonances have been observed throughout the temperature range, corresponding to the two chemically inequivalent chlorine sites. Using Bayer's theory and Brown's method torsional frequencies and their temperature dependence in this range are estimated.Chloro-substituted phenols form an interesting class of compounds and have been the subject of several studies employing nuclear quadrupole resonance (I ). In this paper, we report the results of our measurements on the temperature dependence of the chlorine NQR frequency in 3,4-dichlorophenol in the range 77 to 298 K. The resonance frequencies in 3,6dichlorophenolwere reported earlier by Pies and Weiss (I) at 77 K, 195 K, and room temperature. Two lines are present throughout the temperature range studied, indicating that there are two chemically inequivalent chlorines.In this work, a frequency modulated, self-quenched superregenerative spectrometer was used for detecting the resonances. The resonance frequencies were measured with a BC-221 frequency meter with an accuracy of r 1 kHz and the temperatures were measured with a copper-constantan thermocouple with an accuracy of 20.5 K.
METHOD OF CALCULATIONAccording to Bayer's theory (2), the temperature dependence of an NQR frequency (for I = 3/2 and n = 0) is given by UT = Yo [II where i = X, Y, Z denote the principal EFG axes, the Z axis is taken along the C-Cl direction, the Y axis is taken perpendicular to the 2 axis and lies in the plane 41