Nuclear Quadrupole Resonance Study of Molecular Motion and Intermolecular Forces in Solid Chlorine

Abstract

Nuclear quadrupole resonance frequencies of 35 Cl and 37 Cl in solid chlorine were measured between 20°K and its triple point 172°K. The spectrum consists of a doublet at low temperatures because of isotopic splitting. The results were analyzed in terms of temperature-dependent libration frequencies in a quasi-harmonic approximation. The quadrupole coupling constant for 35 Cl was found to be 108.975±0.003 Mc/sec at 0°K and 109.872±0.010 Mc/sec for the static lattice. The librational frequency was 90.1±3.0 cm -1 at 0°K decreasing to 74.3 cm -1 at 160°K. The lower limit to the asymmetry of the electric field gradient was 8.5% in comparison to bromine (20%) and iodine (17.5%), showing the existence of some covalent character in the intermolecular forces. Some problems concerning the intermolecular potential in solid and gaseous chlorine are pointed out in connection with the re-analysis of the second virial coefficient.