CCL: question about nitro groups in AMBER



In AMBER each atom has a designated type which is defined to set of
 parameters
 in AMBER.  It appears that nitro groups are not able to be characterized by
 the existing atom type definitions.  Are NO2 groups able to be studied with
 AMBER?  Have the parameters for NO2 been determined previously?  Is it
 possible to define your own parameters manually and if so how?  Is there a
 systematic method to how parameters are defined in AMBER?  Any assistance
 would be greatly appreciated.
 Ken Hunter
 Mount Allsion University