NITROGEN NUCLEAR-QUADRUPOLE INTERACTIONS IN RDX, BETA-HMX AND COCAINESYSTEMS

Using the Hartree-Fock-Roothaan procedure, the nuclear quadrupole inte ractions (NQI) of the N-14 (I = 1) nucleus in the energetically import ant molecules RDX, beta-HMX and the physiologically important molecule Cocaine, are studied. The coupling constants (e(2) q Q) and asymmetry parameters (eta) for the three ring nitrogens in RDX are found to be - 5.671, - 5.808 and - 5.838 MHz and 0.542, 0.556 and 0.562, respectiv ely, in good quantitative agreement with the experimental results of 5 .735, 5.799 and 5.604 MHz for the magnitudes of e(2) q Q and 0.6215, 0 .6146 and 0.6024 for eta obtained in the single crystal. For beta-HMX, where two sets of e(2) q Q and eta are expected from symmetry conside rations, our calculated values are - 5.936 and - 6.069 MHz for e(2) q Q and 0.432 and 0.490 for eta, compared to experimentally measured mag nitudes of 5.791 and 6.025 MHz and eta-values of 0.4977 and 0.5180, re spectively, obtained in the single crystal. For Cocaine free base whic h contains only one N-14 nucleus, our calculated values of e(2) q Q an d eta are - 5.038 MHz and 0.067, in very good agreement with the exper imental results of 5.0229 MHz for the magnitude of e(2) q Q and 0.0395 for eta. Possible reasons for the small remaining differences between theory and experiment in e(2) q Q and eta for all three systems and t he significant differences in trends over the three nitrogens in RDX b etween theory and experiment are discussed. Also, the calculated quadr upole interaction parameters for the N-14 nuclei in the NO2 groups out side the ring for both RDX and beta-HMX are presented with the hope th at they will be measured in the future to provide a more complete unde rstanding of the electron distributions in these systems.