PARM94 for DNA, RNA and prot. modified for amidates. Use 1-4 scee 1.2.
Dec,97
MASS
NS 14.01                             sp3 N in amidates 

BOND
CT-NS  320.0    1.440       phosphoramidates 
H -NS  434.0    1.000       phosphoramidates (ab inito opt)
NS-P   230.0    1.710       PHOSPHORAMIDATE

ANGLE
CT-CT-NS    50.0      109.50    phosphoramidates
H1-CT-NS    50.0      109.50    phosphoramidates 
CT-NS-H     35.0      109.50    phosphoramidates 
CT-NS-P    100.0      118.00    phosphoramidates (ab initio geom. data)
H -NS-P     40.0      109.50    phosphoramidates
NS-P -OS    45.0      100.50    phosphoramidates (ab initio geom. data)
O2-P -NS   100.0      108.23    phosphoramidates (ab initio geom. data) 
H1-CT-N3    50.0      109.50    model mol with NH3+
H -NS-H     35.0      109.50    model mol with NH2

DIHEDRAL
X -NS-P -X    6    0.75          0.0             3.        
phosphoramidates 
X -CT-NS-X    6    1.00          0.0             3.        
phosphoramidates 
OS-CT-CT-NS   1    0.14          0.0            -3.        
phosphoramidates
OS-CT-CT-NS   1    0.00          0.0             2.        
phosphoramidate
NS-P -OS-CT   1    0.25          0.0            -3.        
phosphoramidates
NS-P -OS-CT   1    0.60          0.0             2.        
phosphoramidate
CT-NS-P -OS   1    0.125         0.0            -3.
CT-NS-P -OS   1    0.60          0.0             2.        
H -NS-P -OS   1    0.125         0.0            -3.
H -NS-P -OS   1    0.60          0.0             2.

IMPROPER
CT-P -NS-H          0.00         180.0         2.            don't
need,N-sp3

NONB      RE
  NS          1.8750  0.1700             OPLS

END
NS more like N3