C   Jan Labanowski, Aug 13, 1992 
C   This "program" calculates geometrical parameters of the amino group
C   suitable for constructing Z-matrix
C   The experimental data from microwave spectroscopy for something-C-NH2
C   are frequently given as a N--H bond lenth, C--N--H angle and H--N--H
C   angle. Depending where you start, you need some dummy atoms to build
C   the molecule. This programs gives you a few parameters you might use.
C   
C   Input: 
C   d = N--H bond length, thCNH angle C--N--H, thHNH angle H--N--H
C
C   Output:
C   a = distance H....H (the base of the H--N--H isosceles)
C   v = the height of the H--N--H isosceles (i.e., v is the bisector of
C       the H--N--H angle). It starts at C and ends at point Y. Point Y
C       is located half way between H atoms.
C   l = distance N--X (X is the projection of Y on the line passing through
C        C--N). l is a projection of v on the C--N line.
C   h = is the distance from Y to X. (h and l are perpendicular,
C       h is a bisector of the H--X--H angle).
C   b = H--X distance, i.e. distance of the point half way between H atoms
C       and C--N line
C   alpha = C--N--Y angle (angle between C--N bond and v).
C   beta = half of H--X--H angle, i.e. half of the dihedral angle between
C          two CNH planes, i.e., H--X--Y angle.

       PROGRAM AMINO
       DOUBLE PRECISION d, thCNH, thHNH, alpha, h, l, a, v, deg, beta

       WRITE(*,*)
     1 ' Enter N--H bond length, C--N--H angle, H--N--H angle (in deg):'
       READ(*,*)d,thCNH,thHNH
       WRITE(*,*)

       deg = 3.1415926536D0/180.0D0
       a = 2.0D0*d*dsin(0.5D0*thHNH*deg)
C       v = d*dcos(0.5D0*thHNH*deg)
       v = dsqrt(d*d - a*a/4.0D0)
       b = d*dsin((180.0D0-thCNH)*deg)
       h = dsqrt(b*b - a*a/4.0D0)
       l = dsqrt(v*v - h*h)
       alpha = 180.0D0 - dasin(h/v)/deg 
       beta = acos(h/b)/deg

100    FORMAT(1X,A,F10.5)
       WRITE(*,100) 'N--H bond length = ', d
       WRITE(*,100) 'C--N--H angle = ', thCNH
       WRITE(*,100) 'H--N--H angle = ', thHNH
       WRITE(*,100) 'Height of the H--N--H isosceles =', v
       WRITE(*,100) 'H...H distance = ', a
       WRITE(*,100) 
     1 'Projection of H--N--H bisector on the C--N line = ', l
       WRITE(*,100)
     1 'Distance between H...H midpoint and C--N line = ', h
       WRITE(*,100)
     1 'Angle between C--N bond and bisector of H--N--H = ', alpha
       WRITE(*,100)
     1 'Half of dihedral angle between C--N--H planes = ',beta
       WRITE(*,100)
     1 'Distance between H atom and C--N line = ', b

       STOP
       END