## Presentation of two-pulse MAS applet panel

This applet allows us to simulate the two-step experiment
described in the introduction web page. Only the **first-order
quadrupole interaction for powder sample rotating at the
magic angle** is taken into account during the pulses.

The left-hand part of the simulation panel indicates the physical parameters. It is initialized for a spin I = 3/2 in a powder sample. We can select another half-integer quadrupole spin (5/2, 7/2, or 9/2) with the first choice box.

**First**, we provide the rotor
spinning speed, the strength of the RF
magnetic field of the NMR probe, and the quadrupole coupling
constant QCC of the sample in
**kHz unit** using the corresponding text fields. We also select
the asymmetry parameter eta
of the sample with the corresponding choice box.

**Second**, we select one of the two steps for the optimization
of the central-line intensity with the middle choice box.

(i) **A()B(p2):** the first step where p1 is constant
and p2 is variable;

(ii) **A(p1)B():** the second step where p1 is variable
and p2 is constant.

**Third**, we provide a pulse length in the
Min PulseLength text field for
the constant pulse, the last pulse length of the variable pulse in the
Max PulseLength text field, and
the increment of the variable pulse in the Pulse
Increment text field in **Âµs unit**.
The pulse length to pulse increment
ratios must be integers.

**Fourth**, we select the number of integration steps
for alpha and for beta Euler angles with the
MaxAlpha choice box.
We also provide that for gamma Euler angle in the
MaxGamma text field.

**Fifth**, we select the two multiquantum coherences
excited by the first pulse with the Pulse-1
Excites Coherences choice box located at the bottom
of the middle part of the simulation panel.

**Finally**, we press the red Run
button to start the simulation. As a result, this button becomes
the Stop button and the
progress bar, located on the
right-hand side of the red button, starts. We can press the
Stop button at any moment to interrupt the simulation.

**At the end of the simulation**, the central-line intensity
versus the variable pulse length will appear as numerical data
in the corresponding text areas as well as a graph on the
right-hand part of the simulation panel. These numerical data can
be pasted into a spreadsheet software such as MS EXCEL.