Quasar computing module (introduced in dmfit 2005 version)
Jean-Paul Amoureux; UCCS, CNRS-8181, Lille, France

The QUASAR module, computing on/off angle spectra in static or MAS with multiple interactions has been written by Jean Paul Amoureux
please ackownledge him as : Jean-Paul Amoureux; UCCS, CNRS-8181, Lille, France

Quasar determines the signal that can be observed with powder samples, after a perfect p/2 pulse with very large RF-amplitude (much larger than all microscopic interactions).

  • The sample can be static, or in rotation about one axis (VAS, or MAS).

  • Only one RF irradiation is performed: the other nuclei are indeed not manipulated.

  • Microscopic molecular reorientations are assumed to be negligible.

  • Hamiltonians are calculated using the AHT theory, without any non-secular terms.1

  • Possible interactions are : CSA (1st-order), quadrupole interaction (2nd-order); hetero-nuclear scalar and dipolar interactions to the 1st-order.

  • 2nd-order cross-terms (quadrupole with CSA or dipolar) are not introduced.

All interactions are described with respect to the CSA (spin = ½), or the quadrupole (spin > ½) tensor. The relative orientations of the different interactions with respect to the CSA (or quadrupole) tensor are described with 3 Euler angles, according to the definition of M. Mehring.2 and in agreement with definitions used by SIMPSON.

In the case of the uniaxial dipolar interaction, only 2 polar angles are needed. The description of isotropic scalar couplings, only requires their J values.

1 - M. Goldman, PJ. Grandinetti, A. Llor, Z. Olejniczak, JR. Sachleben, JW. Zwanziger, J. Chem. Phys. 97, 8947-8960, 1992.
2 - M. Mehring, Springer-Verlag 1983.