Isotope Effect of the Pure 35Cl and 37Cl Quadrupole Resonance Spectra in CHCl2COOH and CDCl2COOD

Abstract

Abstract The temperature dependence of the pure nuclear quadrupole resonance of 35Cl and 37Cl in solid CHCl2COOH and CDCl2COOD has been measured. The spectra are doublets according to two dif­ferent sites, Cl (I) and Cl (II), of the chlorine atoms in the CXCl2 group (X = H,D). In CHCl2COOH and CDCl2COOD the 37Cl spectra became unobservable above 198 K and 175 K and the 35Cl spectra vanished at 238 K and 226 K, respectively. The temperature dependence was calculated using the Bayer-Kushida theory which gives a satisfactory approach in the case of the compounds investigated here. A small difference has been found in the temperature dependence of the resonance frequen­ cies for CI (I) and CI (II) in both the CHCl2 and CDCl2 group, which is probably due to differences in the bond lengths of CI (I) and CI (II). Furthermore, there is a different temperature dependence of the resonance frequencies of the chlorine isotopes at the sites CI (I) and CI (II). This gives evi­ dence for the so-called isotope effect: i. e. there are slightly different thermal motions for the chlorine isotopes which are involved in the averaging of the electric field gradient tensor. The re­ placement of protons by deuterons gave a shift of the resonance frequencies of about 20 kHz to lower values. This may be primarily caused by effects of deuteration on the electronic structure.