gcosy.m

Horne-Morris gradient-selected COSY pulse sequence. The Liouvillian is assembled as L=H+i*R+i*K, the evolution time step is the reciprocal of the sweep width, the initial condition is Lz on the working spins and the detection state is L+ on the same spins. A 90-degree pulse about Lx is followed by the F1 evolution, run as a trajectory with npoints(1)-1 steps. The mixing propagator is the recovery delay that follows the first gradient, applied first, followed by the pulse at parameters.angle; that composite propagator is placed between the two gradients by grad_sandw.m function, both gradients having the duration in parameters.g_dur and acting over the sample length in parameters.s_len, and a further stabilisation delay is run after the second gradient. The F2 dimension is then detected with npoints(2)-1 steps. The function requires the sphten-liouv formalism.

The two gradients have opposite signs for the P-type pathway and equal signs for the N-type one. In the 'P+N' mode both gradient sandwiches are applied to the same F1 stack and detected separately, so that the echo and the anti-echo components are returned together.

Syntax

    fid=gcosy(spin_system,parameters,H,R,K)

Parameters

    parameters.sweep        sweep width in Hz

    parameters.npoints      number of points for both dimensions

    parameters.spins        nuclei on which the sequence runs,
                            specified as {'1H'}, {'13C'}, etc.

    parameters.angle        second pulse angle in radians, usu-
                            ally pi/2, but also allows COSY45,
                            COSY60, etc.

    parameters.g_amp        gradient amplitude in Gauss/cm,
                            defaults to 3

    parameters.g_dur        gradient duration in seconds,
                            defaults to 2e-3

    parameters.g_stab_del   post-gradient stabilisation delay in
                            seconds, defaults to 2e-4

    parameters.s_len        active sample length in cm,
                            defaults to 1.5

    parameters.pathway      optional coherence pathway selection,
                            either 'P', 'N', or 'P+N', defaults
                            to 'P'

    H  - Hamiltonian matrix, received from context function

    R  - relaxation superoperator, received from context function

    K  - kinetics superoperator, received from context function

Outputs

    fid  - two-dimensional free induction decay, or a structure
           with P-type fid.pos and N-type fid.neg fields in
           'P+N' mode

Examples

A gradient-selected COSY spectrum of strychnine at 5.9 Tesla, run in the 'P+N' mode and processed by echo/anti-echo recombination, is in examples/nmr_liquids/gcosy90_strychnine.m file of the standard distribution.

Notes

Note: the default P-type pathway uses opposite gradient signs and is less sensitive to mixing pulse phase errors. The N-type pathway uses equal gradient signs.

Note: 'P+N' mode returns P-type and N-type components for echo/anti-echo recombination in phase-sensitive processing.

See also

cosy.m, dqf_cosy.m, ct_cosy.m, grad_sandw.m, Built-in experiments

Version 2.13, authors: Ilya Kuprov