%chk=nh3_scan.chk
%mem=500MB
%nproc=1
#opt=z-matrix nosymm b3lyp/6-311G(d,p)

scan barrier to inversion for nh3 

0 1
 X  
 N  1   2.0
 H  2   R1   1   A1
 H  2   R1   1   A1   3   T1
 H  2   R1   1   A1   3  -T1

 R1     1.01
 A1     90.0   S  20 -2.0 
 T1     120.0