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

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.