The half-gaussian shape was presented as a useful alternative to gaussian shape because does not create significant amounts of antiphase magnetization, but leads almost quantitatively to in-phase magnetization of the selected signal.

The half-gaussian shape can be generated in the SHAPE tool.

Half-gaussian shapes pulses were originally proposed to achieve selective excitation of single multiplet lines ( 87JMR390-75 ). However, while the absorptive part of the excitation profile shows an excellent selectivity, its dispersive mode component has a unacceptably large band width that must be removed. This is usually achieved by applying a non-selective 90_y,-y degree pulse immediately after the half-gaussian pulse. Application in selective 1D and 2D experiments requiring in-phase components was reported ( 89JMR1-85 ).

More details in Tutorials: Defining a Half-gaussian shape.

The theoretical excitation profile of a half-gaussian shaped 90 degree pulse can be visualized from the NMRSIM program:
 
1. Select the corresponding File-->Experiment Setup-->Load from File ... menu.
2. Choose the profile.cfg configuration file.
3. Set the shape to hgauss3.shp in the Go-->Check Experiment parameters menu.
4. Select the Go-->Run Experiment menu.
5. The result of the simulation is displayed in the nmrsim 1 1 file into the XWIN-NMR window. Transform the data with ef (lb=1).
6. The duration of the shaped pulse can be modified by changing the P5 parameter (by default, 5 ms) in the Go-->Check Experiment parameters menu. Repeat the 4 and 5 steps to obtain the new profile.