spin = 3/2;
(* parameters of the quadrupole interaction *)
alphaQ = 0; betaQ = 0; gammaQ = 0; eta = 0; cQ = 2*(2*Pi)*28.1*10^6;
(* parameters of the Zeeman interaction *)
wL = 2*10^4; thetaZ = 0; phiZ = 0;
(* parameters of the RF interaction *)
w1 = 1*10^5; wRF = 2*(2*Pi)*28.1*10^6; thetaRF = Pi/2; phiRF = 0; phase = 0;   H0 = HQ[spin] + HZ[spin]; (* non-perturbed Hamiltonian *)
  H1 = HRF[spin]; (* RF Hamiltonian *)
  TP = Pi/(2*w1); (* duration of the pulse *)
    rho = Pulse[-H0];

(* Fourier transform of the signal detected by a coil in the x-axis *)
thetaDet = Pi/2; phiDet = 0; (* orientation of the detection coil *)
relaxation = 300; (* relaxation rate *)
  fourier = FourierAbs[rho];

(* plot of the spectrum *)
f = fourier /. w -> (1000*(2*Pi)*freq - wRF);
  Plot[f, {freq,-10,10},
   PlotRange->All, Axes->None,
   FrameLabel->"kHz", Frame->{{False,False},{True,False}}]